calibration and testing of upland hillslope evolution models in a dated landscape banco bonito new mexico 1 in this study we tested upland hillslope evolution models and constrained the rates of regolith production colluvial transport and eolian deposition over geologic time scales in a dated volcanic landscape in northern new mexico using field measurements of regolith thickness geochemical analyses of regolith bedrock and regional dust numerical modeling of regolith production and transport and quantitative analyses of airborne light detection and ranging lidar digital elevation models dems within this volcanic landscape many topographically closed basins exist as a result of compressional folding and explosion pitting during eruption the landscape has evolved from an initial state of no regolith cover at 40 5 ka to its modern state which has highly weathered regolith ranging from 0 to 3 m with local thickness values controlled primarily by topographic position our models constrain the maximum rate of regolith production in the study area to be in the range of 0 02 to 0 12 m kyr 1 and the rate of colluvial transport per unit slope gradient to be in the range of 0 2 to 2 7 m 2 kyr 1 with higher values in areas with more aboveground biomass we conclude that a depth dependent colluvial transport model better predicts the observed spatial distribution of regolith thickness compared to a model that has no depth dependence this study adds to the database of estimates for rates of regolith production and transport in the western united states and shows how dated landscapes can be used to improve our understanding of the coevolution of landscapes and regolith cover

clustering river profiles to classify geomorphic domains the structure and organization of river networks has been used for decades to investigate the influence of climate and tectonics on landscapes the majority of these studies either analyze rivers in profile view by extracting channel steepness or calculate planform metrics such as drainage density however these techniques rely on the assumption of homogeneity that intrinsic and external factors are spatially or temporally invariant over the measured profile this assumption is violated for the majority of earth s landscapes where variations in uplift rate rock strength climate and geomorphic process are almost ubiquitous we propose a method for classifying river profiles to identify landscape regions with similar characteristics by adapting hierarchical clustering algorithms developed for time series data we first test our clustering on two landscape evolution scenarios and find that we can successfully cluster regions with different erodibility and detect the transient response to sudden base level fall we then test our method in two real landscapes first in bitterroot national forest idaho where we demonstrate that our method can detect transient incision waves and the topographic signature of fluvial and debris flow process regimes and second on santa cruz island california where our technique identifies spatial patterns in lithology not detectable through normalized channel steepness analysis by calculating channel steepness separately for each cluster our method allows the extraction of more reliable steepness metrics than if calculated for the landscape as a whole these examples demonstrate the method s ability to disentangle fluvial morphology in complex lithological and tectonic settings

a comparative study of suction stress between sand and silt under unsaturated conditions abstract the purpose of this study is to estimate and compare suction stress between sand and silt sampled from the coast of korea the water content and matric suction of sand joomunjin and silt saemangeum were first examined using an automated soil water characteristic curve swcc apparatus based on the axis translation technique swccs were then estimated from the test results using the van genuchten 1980 model at equal matric suction the corresponding water content of silt was higher than that of sand moreover the saturated water content and air entry value aev of silt were larger than those of sand using the fitting swcc parameters suction stress characteristic curves ssccs were estimated according to the method proposed by lu and likos 2006 the sscc behavior for sand and silt was different and significantly depended on the material properties particularly pore size and pore size distribution for sand the suction stress exhibited rapid variation with changes in matric suction but for silt the suction stress approached a constant value as the matric suction increased in addition when the matric suction was smaller than the aev of soil the suction stress was equal to the magnitude of the matric suction in contrast when the matric suction exceeded the aev of soil suction stress had a nonlinear shape with respect to the matric suction

constraining climatic controls on hillslope dynamics using a coupled model for the transport of soil and tracers application to loess mantled hillslopes south island new zealand 1 landscapes reflect a legacy of tectonic and climatic forcing as modulated by surface processes because the morphologic characteristics of landscapes often do not allow us to uniquely define the relative roles of tectonic deformation and climate additional constraints are required to interpret and predict landscape dynamics here we describe a coupled model for the transport of soil and tracer particles at the hillslope scale to illustrate the utility of this methodology we modeled the evolution of two synthetic hillslopes with identical initial and boundary conditions but different histories of climate induced changes in the efficiency of soil transport while one hillslope experienced an initial phase of rapid transport followed by a period of retarded transport the other hillslope experienced the opposite sequence both model hillslopes contain a subsurface layer of tracer particles that becomes exhumed and incorporated into the soil due to transport and mixing processes whereas the morphology of the two model hillslopes cannot be easily distinguished at the simulation conclusion the spatial distribution of tracer particles along the slope is distinctive for the two cases we applied the coupled model to our study site along the charwell river south island new zealand where tephra deposits within loess dominated soils have been exhumed and incorporated into an upper layer of bioturbated and mobile soil we reconstructed the late pleistocene hillslope geometry using soil stratigraphic data gathered along the study transect because bioturbation appears to be the predominant transport mechanism the efficiency of soil transport likely varies with time reflecting the influence of climate related changes in the dominant floral or faunal community the modeled evolution of hillslope form and tephra concentration along the study transect is consistent with observations obtained from topographic surveys and laboratory analysis of tephra concentrations in continuous core soil samples low transport rates are apparently associated with grass shrub dominated slopes during the late pleistocene whereas forest colonization during the holocene increased flux rates transforming flat locally incised slopes into broadly convex ones our results attest to the utility of coupled models for tasks such as deciphering landscape history and predicting the downslope flux of soil organic carbon

carbon dioxide reaction processes in a model brine aquifer at 200 c and 200 bars implications for geologic sequestration of carbon the reactive behavior of supercritical co2 under conditions relevant to geologic storage and sequestration of c is largely unknown experiments were conducted in a flexible cell hydrothermal apparatus to determine the extent of fluid rock reactions in addition to carbonate mineral precipitation that may occur in a brine aquifer aquitard system that simulates a saline aquifer storage scenario the system was held at 200 c and 200 bars for 59 days 1413 h to approach steady state then injected with co2 and allowed to react for another 80 days 1924 h in addition to magnesite precipitation silicate minerals quartz plagioclase microcline and biotite in the aquifer and the aquitard display textures etch pits mineralization indicating significant reaction changes in elemental abundances in the brine following addition of co2 include ph decrease and enrichment in cl partly due to supercritical co2 desiccation of the brine geologic sequestration systems have potential for geochemical reactions that extend beyond simple aqueous dissolution of co2 and precipitation of carbonate these reactions may produce geochemical and geotechnical consequences for sequestration and provide important characteristics for monitoring and evaluation of stored co2 a n understanding of multi phase equilibrium relationships between supercritical co2 and aquifer brine systems also raises new questions for a variety of geologic systems multi phase fluid equilibria may for example account for the large amounts and heterogeneous distributions of calcite cement in a wide variety of geologic systems particularly in sedimentary basin sandstones published by elsevier science ltd

controls of climate topography vegetation and lithology on drainage density extracted from high resolution topography data summary mark melton in 1957 found that climate basin morphometry and surficial variables control drainage density d d but differences observed between field surveyed channels and those mapped on topographic contours or blue lines left doubts on these results later several landscape evolution model and observational studies analyzed the behavior of d d however only a few studies have been performed over a large number of landscapes of different characteristics and have relied on high resolution topography data we revisit melton s hypothesis by using meter resolution digital terrain models dtms in 101 subbasins in the usa we first propose a dimensionless drainage density d dd metric based on the ratio of likely channelized pixels to total number of basin pixels which has the advantage of eliminating the computation of the channel network our analysis shows that d dd is a weak scaling function of the input dtm resolution compared to the classic dimensional d d metric ratio of total channel length to total basin area we analyze the correlation of d dd and mean annual precipitation map with a gaussian mixture model which identifies two sub groups displaying different correlation negative in arid and semi arid environments and positive in humid environments the transition in correlation is around 1100 100 mm yr of map and is accompanied by the occurrence of thick soil layers and high available water capacity that promote dense vegetation cover v cov and low d dd while small variation in d dd is observed across vegetation types increasing v cov corresponds to decreasing d dd we also explore the relationship between d dd and relief r and d dd and lithology d dd and r are weakly correlated in arid and semi arid environments while they have strong positive correlation in humid environments no significant correlation is found between d dd and lithology although the results are likely affected by our sample choice

dynamic processes of co2 storage in the field 1 multiscale and multipath channeling of co2 flow in the hierarchical fluvial reservoir at cranfield mississippi

shallow gravity driven flow in a poro elastic layer by combining biot s theory of poro elasticity with standard shallow layer scalings a theoretical model is developed to describe axisymmetric gravity driven flow through a shallow deformable porous medium motivated in part by observations of surface uplift around co2 sequestration sites the model is used to explore the injection of a dense fluid into a horizontal deformable porous layer that is initially saturated with another less dense fluid the layer lies between a rigid base and a flexible overburden both of which are impermeable as the injected fluid spreads under gravity the matrix deforms and the overburden lifts up the coupled model predicts the location of the injected fluid as it spreads and the resulting uplift of the overburden due to deformation of the solid matrix in general the uplift spreads diffusively far ahead of the injected fluid if fluid is injected with a constant flux and the medium is unbounded both the uplift and the injected fluid spread in a self similar fashion with the same similarity variable r t1 2 the asymptotic form of this spreading is established results from a series of laboratory experiments using polyacrylamide hydrogel particles to create a soft poro elastic material are compared qualitatively with the predictions of the model

tensile strength characteristics of unsaturated sands tensile strength characteristics of unsaturated sands are examined through a combined theoretical and experimental study the characteristics of tensile strength in all three water retention regimes of pendular funicular and capillary are examined a simple direct tensile strength apparatus is employed to determine tensile strength for sands with a broad range of particle sizes from silty sand to fine sand and medium sand over a full range of degree of saturation tensile strength characteristic curves tscc are established experi mentally for these sands and are used to validate the existing theories for tensile strength in the pendular regime the tscc for sand characteristically exhibits two zeros at 0 and near 100 saturation and two peak values occurring in the pendular and capillary regimes respectively a minimum tensile strength is observed in the dense fine sand indicating that either water bridges or pore pressure contributes exclusively to the tensile strength in the funicular regime of this sand the maximum tensile strength for the silty sand is 1 448 pa the fine sand is 1 416 pa and the medium sand is 890 pa comparison between the soil water characteristic curves obtained for these sands indicates that the peak tensile strength in the capillary regime is highly correlated to the air entry pressure photographs of the failure surfaces clearly delineate distinct geometric characteristics for different water retention regimes analysis of the patterns of failure surfaces in different water retention regimes indicates that the effective stress principle is valid for tensile stress failure in unsaturated sands

physics and seismic modeling for monitoring co2 storage we present a new petro elastical and numerical simulation methodology to compute synthetic seismograms for reservoirs subject to co2 sequestration the petro elastical equations model the seismic properties of reservoir rocks saturated with co2 methane oil and brine the gas properties are obtained from the van der waals equation and we take into account the absorption of gas by oil and brine as a function of the in situ pore pressure and temperature the dry rock bulk and shear moduli can be obtained either by calibration from real data or by using rock physics models based on the hertz mindlin and hashin shtrikman theories mesoscopic attenuation due to fluids effects is quantified by using white s model of patchy saturation and the wet rock velocities are calculated with gassmann equations by using an effective fluid modulus to describe the velocities predicted by white s model the simulations are performed with a poro viscoelastic modeling code based on biot s theory where viscoelasticity is described by generalizing the solid fluid coupling modulus to a relaxation function using the pseudo spectral method which allows general material variability a complete and accurate characterization of the reservoir can be obtained a simulation that considers the utsira sand of the north sea illustrates the methodology

dynamic fluid connectivity during steady state multiphase flow in a sandstone abstract the current conceptual picture of steady state multiphase darcy flow in porous media is that the fluid phases organize into separate flow pathways with stable interfaces here we demonstrate a previously unobserved type of steady state flow behavior which we term dynamic connectivity using fast pore scale x ray imaging we image the flow of n2 and brine through a permeable sandstone at subsurface reservoir conditions and low capillary numbers and at constant fluid saturation at any instant the network of pores filled with the nonwetting phase is not necessarily connected flow occurs along pathways that periodically reconnect like cars controlled by traffic lights this behavior is consistent with an energy balance where some of the energy of the injected fluids is sporadically converted to create new interfaces

on the use of seismic data to monitor the injection of co2 into a layered aquifer abstract one method to monitor the migration of co2 through a confined layered aquifer is to use time lapse seismic reflection data we examine how such information may be combined with a flow model for a co2 plume spreading through a water saturated aquifer to provide constraints on the migration of a plume of injected co2 we focus on the estimation of the partitioning of the injected flux between the different layers in a multi layer geological formation and on estimation of the permeability of each layer since there is a minimum depth of the injected co2 which is detectable seismically we show that even in a one layer formation the model predicts two different possible permeabilities for the formation corresponding to a fast pressure driven flow and a slower buoyancy controlled flow these two estimates of the permeability are sensitive to changes in the seismic detection threshold if there is additional data on the bottom hole well pressure we can distinguish between the solutions in a multi layer system supplied from a single well the non uniqueness in the inversion process leads to uncertainty in both the partitioning of the flux between the layers and the permeability of the different layers in the formation the model constraints lead to a relatively small range of possible distributions of the flux but if there is a lack of information about the relative pressure in the different layers near the well there is a much larger range of possible values for the permeability of each layer we develop some simple bounds on the problem by considering the case in which the near well pressure difference between the layers is related to either the vertical hydrostatic or the vertical co2 static pressure difference we examine the implications of the technique for interpreting the historic data set relating to co2 injection at the sleipner field north sea in which there are nine distinct layers in the formation this leads to estimates for the possible flux partitioning between the layers and also some constraints on the possible range of effective permeability in each layer estimates of the partitioning of the flux can inform estimates of the efficiency of co2 injection in the different layers however the uncertainty in the estimate of the effective permeability leads to uncertainty in estimates of the propagation speed of the flow in each layer and hence assessments of the hazards of leakage and of the rate of capillary trapping or dissolution of co2 following injection

drainage density slope angle and relative basin position in japanese bare lands from high resolution dems abstract relationships between drainage density and slope angle for three bare lands in japan were analyzed with special attention to channels at early erosion stages and channels in a badland type terrain two of the bare lands were caused by volcanic eruptions 1 or 30 40 years ago and the other one is a landslide scar formed more than 100 years ago raster digital elevation models dems with a 1 m resolution and ortho aerial photos were generated using digital photogrammetry to enable detailed stream net extraction and topographic analyses data for drainage density slope angle and relative height for 88 subwatersheds were obtained from the dems and derived stream nets the relationship between drainage density and slope angle for each subwatershed can be divided into two types downward sloping and convex upward although previous studies suggested that drainage density positively correlates with slope angle if overland flow is dominant this correlation seldom occurs in the study areas the two types of drainage density slope angle relationships correspond to differing channelization stages that reflect the extension and integration of existing channels as well as the formation of new low order streams in response to base level lowering the location of subwatersheds within each study area seems to play a major role in determining the stages of channel development and in turn the types of drainage density slope angle relationships

channel networks a geomorphological perspective the study of channel networks has been dominated since 1966 by the random model however recent work has shown 1 that although the topological properties of small networks conform to the random model more closely than those of large ones even small networks exhibit systematic deviations from topological randomness and 2 that the topological and length properties of channel networks are controlled to a large degree by the spatial requirements of subbasins and the need for these subbasins to fit together in space by the size sinuosity and migration rate of valley bends and by the length and steepness of valley sides the factors that control the density properties of channel networks vary with the scale of the investigation and the geomorphic processes governing channel initiation although progress has been made toward a satisfactory stream junction angle model further work is needed the evolution of channel networks has been investigated by a variety of methods including the development of conceptual and simulation models the monitoring of small scale badland and experimental drainage basins and the substitution of space for time the morphology of most channel networks is largely inherited from the past or strongly influenced by inherited forms inasmuch as there is no way of ever knowing the origin or complex history of such networks the use of stochastic models in their study seems unavoidable

noble gas and carbon isotopic evidence for co2 driven silicate dissolution in a recent natural co2 field secure storage of anthropogenic carbon dioxide co2 in geological reservoirs requires predicting gas water rock interactions over millennial timescales noble gases and carbon isotope measurements can be used to shed light on the nature of competing dissolution precipitation processes over different timescales from the fast dissolution of gaseous co2 in groundwater to more sluggish reactions involving dissolution and precipitation of newly formed minerals in the reservoir here we study a compilation of gas analyses including noble gases and 13c of co2 from nine different natural co2 reservoirs amongst these reservoirs the bravo dome co2 field new mexico usa shows distinct geochemical trends which are explained by degassing of noble gases from groundwater altering the composition of the gas phase this groundwater degassing is synchronous with the dissolution of co2 in groundwater progressive creation of alkalinity via co2 promoted mineral dissolution is required to explain the observed positive correlation between co2 3he and 13c of the gas phase a unique feature of bravo dome the differences between bravo dome and other natural co2 reservoirs are likely explained by the more recent filling of bravo dome reflecting co2 water rock interactions over thousands of years rather than over millions of years in older reservoirs

paleogeographic setting and depositional architecture of a sand dominated shelf depositional system miocene utsira formation north sea basin abstract the middle late miocene utsira sandstone of the north sea basin contains a fully preserved regional marine sand deposit that records a stable paleogeographic setting of shelf sand transport and accumulation within an epeiric shelf sea which persisted for ca 8 myr the sediment dispersal system was defined by 1 sediment input through a prograding strandplain platform coast to shelf bypass and regional basin centered transport and deposition within an elongate seaway 2 a high energy marine regime 3 very low rates of sediment supply and accumulation in the accommodation dominated seaway 4 high sediment reworking ratio and consequent abundance of autochthonous sediment 5 regional along strike sediment transport and 6 local to subregional landward sediment transport shelf systems were primarily nourished by sediment reworked from the shetland strandplain which prograded eastward into the central viking trough the viking strait lay between the constructional platform and the nondepositional horda platform southward longshore transport on the high energy shoreface and shallow shelf platform constructed the mounded south viking shelf shoal southward building sandy banner banks that formed along the recurved arc of the platform margin nourished the shoal system low angle sigmoid clinoforms with downstepping aggradational tops are distinctive architectures of the strike fed sand bodies the combination of strong marine currents and slow but continual sand supply from the shetland strandplain created regional sandy shelf depositional systems that individually covered 3500 to 6000 sq km of basin floor defining elements of the shelf shoal systems include their location within the basin axis mounded morphology stratal architecture and construction by amalgamated marine sand facies

biot dispersion for p and s wave velocities in partially and fully saturated sandstones ultrasonic compressional and shear wave velocities have been measured on 34 samples of sandstones from hydrocarbon reservoirs the sandstones are all of low clay content high porosity and cover a wide range of permeabilities they were measured dry and brine saturated under hydrostatic effective stresses of 10 20 and 40 mpa for eight of the sandstones ultrasonic velocity measurements were made at different partial water saturations in the range from dry to fully saturated the gassmann biot theory is found to account for most of the changes in velocities at high effective stress levels when the dry sandstones are fully saturated with brine provided the lower velocities resulting when the dry sandstone initially adsorbs small amounts of moisture are used to determine the elastic properties of the dry sandstone at lower effective stress levels local flow phenomena due to the presence of open microcracks are assumed to be responsible for measured velocities higher than those predicted by the theory the partial saturation results are modelled fairly closely by the gassmann biot theory assuming heterogeneous saturation for p waves

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

spatial and temporal evolution of injected co2 at the sleipner field north sea time lapse three dimensional 3d seismic surveys have imaged an accumulation of injected co 2 adjacent to the sleipner field in the north sea basin the changing pattern of reflectivity suggests that co 2 accumulates within a series of interbedded sandstones and mudstones beneath a thick caprock of mudstone nine reflective horizons within the reservoir have been mapped on six surveys acquired between 1999 and 2008 these horizons have roughly elliptical planforms with eccentricities ranging between two and four in the top half of the reservoir horizon areas grow linearly with time in the bottom half horizon areas initially grow linearly for about eight years and then progressively shrink the central portions of deeper reflective horizons dim with time amplitude analysis of horizons above within and below the reservoir show that this dimming is not solely caused by acoustic attenuation instead it is partly attributable to co 2 migration and or co 2 dissemination which reduce the impedance contrast between sandstone and mudstone layers growth characteristics and permeability constraints suggest that each horizon grows by lateral spreading of a gravity current this model is corroborated by the temporal pattern of horizon velocity pushdown beneath the reservoir horizon shrinkage may occur if the distal edge of a co 2 filled layer penetrates the overlying mudstone if the buoyant plume draws co 2 upward or if the effective permeability of deeper mudstone layers increases once interstitial brine has been expelled topographic control is evident at later times and produces elliptical planforms especially toward the top of the reservoir our results show that quantitative mapping and analysis of time lapse seismic surveys yield fluid dynamical insights which are testable shedding light on the general problem of co 2 sequestration

sensitivity of watershed attributes to spatial resolution and interpolation method of lidar dems in three distinct landscapes this study investigates scaling relationships of watershed area and stream networks delineated from lidar dems the delineations are tested against spatial resolution including 1 5 10 25 and 50 m and interpolation method including inverse distance weighting idw moving average ma universal kriging uk natural neighbor nn and triangular irregular networks tin study sites include mosquito creek scotty creek and thomas brook representing landscapes with high low and moderate change in elevation respectively results show scale dependent irregularities in watershed area due to spatial resolution at thomas brook and mosquito creek the highest sensitivity of watershed area to spatial resolution occurred at scotty creek due to high incidence of lidar sensor measurement error and subtle changes in elevation length of drainage networks did not show a scaling relationship with spatial resolution due to algorithmic complications of the stream initiation threshold stream lengths of main channels at thomas brook and mosquito creek displayed systematic increases in length with increasing spatial resolution described through an average fractal dimension of 1 059 the scaling relationship between stream length and dem resolution allows estimation of stream lengths from low resolution dems in the absence of high resolution dems single stream validation at thomas brook showed the 1 m dem produced the lowest length error and highest spatial accuracy at 3 7 and 71 3 respectively single stream validation at mosquito creek showed the 25 m dem produced the lowest length error and the 1 m dem the highest spatial accuracy at 0 6 and 61 0 respectively

an inverse method for estimating thickness and volume with time of a thin co2 filled layer at the sleipner field north sea migration of co 2 through storage reservoirs can be monitored using time lapse seismic re ection surveys at the sleipner field injected co 2 is distributed throughout nine layers within the reservoir these layers are too thin to be seismically resolvable by direct measurement of the separation between re ections from the top and bottom of each layer here we develop and apply an inverse method for measuring thick ness changes of the shallowest layer our approach combines di erences in traveltime down to a speci c re ection together with amplitude measurements to determine layer thicknesses from time lapse surveys a series of synthetic forward models were used to test the robustness of our inverse approach and to quantify uncertainties in the absence of ambient noise this approach can unambiguously resolve layer thickness if a realistic ambient noise distribution is included layer thicknesses of 1 6 m are accurately retrieved with an uncertainty of 0 5 m we used this approach to generate a thickness map of the shallowest layer the delity of this result was tested using measurements of layer thickness determined from the 2010 broadband seismic survey the calculated volume of co 2 within the shallowest layer increases at a rate that is quadratic in time despite an approximately constant injection rate into the base of the reser voir this result is consistent with a diminished growth rate of the areal extent of underlying layers finally the relationship between caprock topography and layer thickness is explored and potential migration pathways that charge this layer are identi ed

modelling carbon dioxide accumulation at sleipner implications for underground carbon storage an analytical solution to the equations describing the flow of a buoyant fluid released into a porous medium below a horizontal impermeable boundary is used to model the growth of co2 accumulations beneath thin mudstone beds in the utsira sand reservoir at sleipner in the north sea here supercritical co2 has been injected at a rate of 1 mt yr since 1996 and imaged by time lapse seismic data in 1999 2001 and 2002 the co2 rises as a narrow plume and is partially trapped by a number of thin mudstones before reaching the caprock to the reservoir the radii of the individual layers of trapped co2 increase as the square root of time since initiation as predicted by the modelling for constant input flux however apparent negative initiation times for horizons low in the reservoir suggests that net input fluxes for these layers have decreased with time most probably as the spreading layers have increased their leakage rates accumulation of co2 in the layers higher in the reservoir was initiated up to 3 yr after injection started modelling of the thickness profiles across three of the higher layers suggests that their net input fluxes have increased with time the observation that the central thicknesses of the deeper layers have remained approximately constant or have slightly decreased since first imaged in 1999 is consistent with the model predictions that the central thickness is directly proportional to net input flux however estimates of the permeability of the reservoir from the rate of increase of the radii of the co2 accumulations are an order of magnitude less than measured permeabilities on the reservoir sandstone permeabilities estimated from the modelling of layer thickness changes scatter in the same range these discrepancies may arise from 1 approximations in the model not being valid 2 the measured permeabilities not being representative of the permeability for two phase flow on the scale of the reservoir or considered less likely 3 that much less co2 is being stored in the imaged co2 accumulations than estimated from the seismic reflection profiles the most probable cause of the discrepancy is that the relative permeability for the co2 phase is significantly reduced at lower co2 saturations

modelling carbon dioxide sequestration in layered strata motivated by the geological sequestration of carbon dioxide co2 we study the propagation of gravity currents in a porous medium bounded by a thin layer of much lower permeability we formulate a model for drainage assuming that the fluid remains simply connected throughout using this model we examine the propagation of both two dimensional and axisymmetric currents numerically we find that for the fixed flux situation solutions approach a steady state which is described analytically the approach to this final solution depends on both the permeability contrast and thickness of the thin layer and in many cases the current first overshoots before relaxing back to its ultimate steady state finally we examine propagation along multiple thin lower permeability layers as a reduced order model of the plume of co2 currently being injected at sleipner in the north sea

planform geometry and relief characterization of drainage networks in high relief environments an analysis of chilean andean basins abstract drainage network types give indications of the landscape evolution processes and the lithologic and structural conditions that produced them moreover drainage network attributes affect the hydrologic response of basins several network types have been identified through visual inspection and more recently through quantitative methods developed and applied primarily on relatively low relief regions these methods have not been tested in high relief environments where other factors can control network evolution and other network types may exist in this work we study the occurrence of network types in high relief environments and their potential identification through quantitative classification methods we analyze 29 high relief basins in the chilean andean region after exploring the contextual properties geological climatic and landcover of these networks we calculate several metrics describing their horizontal and vertical attributes and benchmark them against those for network types in low relief regions results show that the high relief networks have three different types herringbone barbed and high relief pinnate which differ in terms of their contextual properties as well as their horizontal and vertical attributes classification trees built using only vertical attributes have accuracies of 93 and 84 when differentiating among the high and low relief networks respectively furthermore an overall accuracy of 91 is reached when classifying the entire set of high and low relief networks with a combination of vertical and horizontal attributes overall we conclude that classification of drainage patterns through vertical and horizontal attributes is feasible and more accurate than with horizontal attributes alone

the effects of bioturbation on soil processes and sediment transport abstract plants and animals exploit the soil for food and shelter and in the process affect it in many different ways for example uprooted trees may break up bedrock transport soil downslope increase the heterogeneity of soil respiration rates and inhibit soil horizonation in this contribution we review previously published papers that provide insights into the process of bioturbation we focus particularly on studies that allow us to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production using geometrical relationships and data from others work we derive simple sediment flux equations for tree throw and root growth and decay

hillslope to valley transition morphology new opportunities from high resolution dtms abstract the search for the optimal spatial scale for observing landforms to understand physical processes is a fundamental issue in geomorphology topographic attributes derived from digital terrain models dtms such as slope curvature and drainage area provide a basis for topographic analyses the slope area relationship has been used to distinguish diffusive hillslope from linear valley processes and to infer dominant sediment transport processes in addition curvature is also useful in distinguishing the dominant landform process recent topographic survey techniques such as lidar have permitted detailed topographic analysis by providing high quality dtms this study uses lidar derived dtms with a spatial scale between 1 and 30 m in order to find the optimal scale for observation of dominant landform processes in a headwater basin in the eastern italian alps where shallow landsliding and debris flows are dominant the analysis considered the scaling regimes of local slope versus drainage area the spatial distribution of curvature and field observations of channel head locations the results indicate that i hillslope to valley transitions in slope area diagrams become clearer as the dtm grid size decreases due to the better representation of hillslope morphology and the topographic signature of valley incision by debris flows and landslides is also best displayed with finer dtms ii regarding the channel head distribution in the slope area diagrams the scaling regimes of local slope versus drainage area obtained with grid sizes of 1 3 and 5 m are more consistent with field data and iii the use of thresholds of standard deviation of curvature particularly at the finest grid size were proven as a useful and objective methodology for recognizing hollows and related channel heads

vegetation modulated landscape evolution effects of vegetation on landscape processes drainage density and topography 1 topography acts as a template for numerous landscape processes that include hydrologic ecologic and biologic phenomena these processes not only interact with each other but also contribute to shaping the landscape as they influence geomorphic processes we have investigated the effects of vegetation on thresholds for channel initiation and landform evolution using both analytical and numerical approaches vegetation is assumed to form a uniform ground cover runoff erosion is modeled based on a power function of excess shear stress in which shear stress efficiency is inversely proportional to vegetation cover this approach is validated using data plant effect on slope stability is represented by additional cohesion provided by plant roots vegetation cover is assumed to reduce sediment transport rates due to physical creep processes rainsplash dry ravel and expansion and contraction of sediments according to a negative exponential relationship vegetation grows as a function of both available cover and unoccupied space by plants and is killed by geomorphic disturbances runoff erosion and landsliding and wildfires analytical results suggest that in an equilibrium basin with a fixed vegetation cover plants may cause a transition in the dominant erosion process at the channel head a runoff erosion dominated landscape under none or poor vegetation cover may become landslide dominated under a denser vegetation cover the sign of the predicted relationship between drainage density and vegetation cover depends on the relative influence of vegetation on different erosion phenomena with model parameter values representative of the oregon coast range ocr numerical experiments conducted using the channel hillslope integrated landscape development child model confirm the findings based on the analytical theory a highly dissected fluvial landscape emerges when surface is assumed bare when vegetation cover is modeled landscape relief increases resulting in hollow erosion dominated by landsliding interestingly our simulations underscore the importance of vegetation disturbances by geomorphic events and wildfires on the landscape structure simulated landscapes resemble real world catchments in the ocr when such disturbances are considered

channel network extraction from high resolution topography using wavelets 1 the availability of high resolution topography from lidar offers new opportunities for objectively extracting the channels directly from a dem using local topographic information instead of inferring them indirectly based on global criteria such as area or area slope threshold relationships here we introduce the use of wavelet filtering to delineate threshold curvatures for defining valleys and threshold slope direction change for defining probable channeled portions of the valleys this approach exploits the topographic signatures uniquely found in high resolution topography and reveals the fuzzy topographic transition in which local weakly convergent areas lie at the transition between hillslopes and valleys

calendar time interpolation of amplitude maps from 4d seismic data a calendar time interpolation method for 2d seismic amplitude maps done in two steps is presented the contour interpolation part is formulated as a quadratic programming problem whereas the amplitude value interpolation is based on a conditional probability formulation the method is applied on field data from the sleipner co2 storage project the output is a continuous image movie of the co2 plume besides visualization the output can be used to better couple 4d seismic to other types of data acquired the interpolation uncertainty increases with the time gap between consecutive seismic surveys and is estimated by leaving a survey out blind test errors from such tests can be used to identify problems in understanding the flow and possibly improve the interpolation scheme for a given case field life cost of various acquisition systems and repeat frequencies are linked to the time lapse interpolation errors the error in interpolated amplitudes increased by 3 4 per year of interpolation gap for the sleipner case interpolation can never fully replace measurements

effect of clay minerals on the suction stress of unsaturated soils abstract the primary objective of this study is to investigate the characteristics of suction stress in two types of unsaturated weathered soils with different clay minerals to obtain the mineralogical properties of the two samples x ray diffraction and scanning electron microscope analyses were conducted and a large amount of kaolinite and montmorillonite was subsequently contained in the granite soil and mudstone soil respectively the granite soil was first remolded to obtain the same relative density and particle size distribution as the mudstone soil and an automated soil water characteristic curve swcc apparatus was used to measure the water content and matric suction the weathered granite soil had a higher air entry value and the volumetric water content was significantly changed by small changes in matric suction the weathered mudstone soil showed a large hysteresis in the swccs between drying and wetting processes because of the ink bottle effect contact angle effect and trapped air the suction stress characteristic curve sscc demonstrates that weathered mudstone soil had a larger magnitude of suction stress the ssccs of the weathered granite and mudstone soils display similar tendencies to the ssccs of silt and clay respectively therefore the unsaturated characteristics considerably depend on the clay mineral composition and particle size distribution

acoustic properties of sediments saturated with gas hydrate free gas and water we obtain the wave velocities and quality factors of gas hydrate bearing sediments as a function of pore pressure temperature frequency and partial saturation the model is based on a biot type three phase theory that considers the existence of two solids grains and gas hydrate and a fluid mixture attenuation is described with the constant q model and viscodynamic functions to model the high frequency behaviour we apply a uniform gas water mixing law that satisfies wood s and voigt s averages at low and high frequencies respectively the acoustic model is calibrated to agree with the patchy saturation theory at high frequencies white s model pressure effects are accounted by using an effective stress law for the dry rock moduli and permeabilities the dry rock moduli of the sediment are calibrated with data from the cascadia margin moreover we calculate the depth of the bottom simulating reflector bsr below the sea floor as a function of sea floor depth geothermal gradient below the sea floor and temperature at the sea floor

pressure and fluid saturation prediction in a multicomponent reservoir using combined seismic and electromagnetic imaging this paper presents a method for combining seismic and electromagnetic em measurements to predict changes in water saturation pressure and co2 gas oil ratio in a reservoir undergoing co2 flood crosswell seismic and em data sets taken before and during co2 flooding of an oil reservoir are inverted to produce crosswell images of the change in compressional velocity shear velocity and electrical conductivity during a co2 injection pilot study a rock properties model is developed using measured log porosity fluid saturations pressure temperature bulk density sonic velocity and electrical conductivity the parameters of the rock properties model are found by an l1 norm simplex minimization of predicted and observed differences in compressional velocity and density a separate minimization using archie s law provides parameters for modeling the relations between water saturation porosity and electrical conductivity the rock properties model is used to generate relationships between changes in

stratigraphy and facies distribution of the utsira formation and the pliocene sequences in the northern north sea abstract the upper cenozoic deposits of the northern north sea have been analysed in order to establish a regional and detailed stratigraphy the utsira formation is subdivided into four log units and mapped and two main depocentres are outlined the lower part of the utsira formation consists of thick marine mounded sand bodies interpreted as overall stacked lowstand fan deposits while the upper part of the formation consists of more clayey silty intervals indicating increased relative sea level the succeeding progradational pliocene deposits are subdivided into 13 high frequency depositional sequences and are mapped the sequences are grouped into four composite sequences each of the four pliocene composite sequences is composed of one or two rather locally distributed prograding sequences lowstand sequence set succeeded by one or two more widely distributed aggrading prograding sequences transgressive highstand sequence set boundaries between the composite sequences are recorded as marked changes in distribution of depocentres and sequence architecture the regional uplift of scandinavia is believed to be the main control on sediment input feeding the succeeding general prograding pliocene sequences oscillations of the eustatic sea level punctuated the tectonically controlled progradation and affected variations in the accommodation space and thus created the high frequency sequences

geologic influences on fluvial hydrology and bedload transport in small mountainous watersheds northern new mexico u s a discharge characteristics in six adjacent mountainous watersheds in northern new mexico u s a vary substantially between basins underlain by different lithologies relatively resistant gneisses and granites underlie two basins drainage areas 43 and 94 km2 that have high unit discharge 0 010 to 0 14 m3s 1 km 2 high bankfull discharge and sustained high discharge less resistant sandstones and shales underlie four basins drainage areas 96 to 215 km2 that have relatively low unit discharge 0 001 to 0 005 m3s 1 km 2 relatively low bankfull discharge and peak discharges that are not sustained as long as those in the crystalline terrane analysis of snowmelt runoff water budgets suggests that three factors control hydrologic conditions in the basins first area elevation distributions appear to control the timing and amounts of water input these distributions probably reflect the erosional resistance of the different lithologies second lithology appears to control runoff production in areas having minor amounts of storage third glacial deposits in headwater regions control discharge duration and timing via storage and return flow releases the amount of return flow released by glacial deposits however is probably controlled by the permeability of underlying bedrock therefore it appears that the duration timing and magnitude of discharge events in the study area are controlled both directly and indirectly by lithology stream power and shear stress estimates derived from bankfull discharge and bed material size data suggest that higher bedload transport rates and larger bedload particle sizes exist in streams draining crystalline rocks than in streams draining sedimentary terrane it appears that source area lithology by controlling discharge production also influences stream power bedload transport capabilities and therefore total amounts of bedload transport

the relationship between drainage density erosion rate and hilltop curvature implications for sediment transport processes drainage density is a fundamental landscape metric describing the extent of the fluvial network we compare the relationship between drainage density dd and erosion rate e using the channel hillslope integrated landscape development child numerical model we find that varying the channel slope exponent n in detachment limited fluvial incision models controls the relationship between dd and e with n 1 resulting in increasing dd with e if all other parameters are held constant this result is consistent when modeling both linear and nonlinear hillslope sediment flux we also test the relationship between dd and e in five soil mantled landscapes throughout the usa feather river ca san gabriel mountains ca boulder creek co guadalupe mountains nm and bitterroot national forest id for two of these field sites we compare dd to cosmogenic radionuclide crn derived erosion rates and for each site we use mean hilltop curvature as a proxy for erosion rate where crn derived erosion rates are not available we find that there is a significant positive relationship between dd e and hilltop curvature across every site with the exception of the san gabriel mountains ca this relationship is consistent with an n exponent greater than 1 suggesting that at higher erosion rates the transition between advective and diffusive processes occurs at smaller contributing areas in soil mantled landscapes

benchmarking of vertically integrated co2 flow simulations at the sleipner field north sea abstract numerical modeling plays an essential role in both identifying and assessing sub surface reservoirs that might be suitable for future carbon capture and storage projects accuracy of flow simulations is tested by benchmarking against historic observations from on going co2 injection sites at the sleipner project located in the north sea a suite of time lapse seismic reflection surveys enables the three dimensional distribution of co2 at the top of the reservoir to be determined as a function of time previous attempts have used darcy flow simulators to model co2 migration throughout this layer given the volume of injection with time and the location of the injection point due primarily to computational limitations preventing adequate exploration of model parameter space these simulations usually fail to match the observed distribution of co2 as a function of space and time to circumvent these limitations we develop a vertically integrated fluid flow simulator that is based upon the theory of topographically controlled porous gravity currents this computationally efficient scheme can be used to invert for the spatial distribution of reservoir permeability required to minimize differences between the observed and calculated co2 distributions when a uniform reservoir permeability is assumed inverse modeling is unable to adequately match the migration of co2 at the top of the reservoir if however the width and permeability of a mapped channel deposit are allowed to independently vary a satisfactory match between the observed and calculated co2 distributions is obtained finally the ability of this algorithm to forecast the flow of co2 at the top of the reservoir is assessed by dividing the complete set of seismic reflection surveys into training and validation subsets we find that the spatial pattern of permeability required to match the training subset can successfully predict co2 migration for the validation subset this ability suggests that it might be feasible to forecast migration patterns into the future with a degree of confidence nevertheless our analysis highlights the difficulty in estimating reservoir parameters away from the region swept by co2 without additional observational constraints

sediment supply and channel morphology in mountain river systems 1 relative importance of lithology topography and climate 1 quantifying landscape scale variations in sediment supply to streams and rivers is fundamental to our understanding of both denudational processes and stream channel morpho dynamics previous studies have linked a variety of sediment supply proxies to climatic topographic or geologic factors but few have connected these directly to the characteristics of fluvial systems draining these landscapes here we correlate landscape controls on sediment supply to observed sedimentology and channel patterns through direct measurements of water and sediment fluxes in over 80 drainage basins ranging in area from 1 4 to 35 000 km2 in the northern rocky mountains usa these data show that the relative sediment supply defined by the bankfull sediment concentration is dominated by basin lithology while exhibiting little correlation to factors such as relief mean basin slope and drainage density bankfull sediment concentrations bed load and suspended load increase as much as 100 fold as basin lithology becomes dominated by softer sedimentary and volcanic rocks relative to basins with more resistant lithologies as bed load concentrations increase stream beds become less armored and bed load grain size coarsens at very high sediment concentrations bed surface subsurface and bed load grain sizes converge and a transition from single thread to to braided channel patterns is commonly observed

on the slow draining of a gravity current moving through a layered permeable medium we examine the gravitational dispersal of dense fluid through a horizontal permeable layer which is separated from a second underlying layer by a narrow band of much lower permeability we derive a series of analytical solutions which describe the propagation of the fluid through the upper layer and the draining of the fluid into the underlying region the model predicts that the current initially spreads according to a self similar solution however as the drainage becomes established the spreading slows and in fact the fluid only spreads a finite distance before it has fully drained into the underlying layer we examine the sensitivity of the results to the initial conditions through numerical solution of the governing equations we find that for sources of sufficiently large initial aspect ratio defined as the ratio of height to length the solution converges rapidly to the initially self similar regime for longer and shallower initial source conditions this convergence does not occur but we derive estimates for the run out length of the current which compare favourably with our numerical data we also present some preliminary laboratory experiments which support the model

multiresolution analysis of characteristic length scales with high resolution topographic data characteristic length scales cls define landscape structure and delimit geomorphic processes here we use multi resolution analysis mra to estimate such scales from high resolution topographic data mra employs progressive terrain defocusing via convolution of the terrain data with gaussian kernels of increasing standard deviation and calculation at each smoothing resolution of i the probability distributions of curvature and topographic index defined as the ratio of slope to area in log scale and ii characteristic spatial patterns of divergent and convergent topography identified by analyzing the curvature of the terrain the mra is first explored using synthetic 1d and 2d signals whose cls are known it is then validated against a set of marssim a landscape evolution model steady state landscapes whose cls were tuned by varying hillslope diffusivity and simulated noise amplitude the known cls match the scales at which the distributions of topographic index and curvature show scaling breaks indicating that the mra can identify cls in landscapes based on the scaling behavior of topographic attributes finally the mra is deployed to measure the cls of five natural landscapes using meter resolution digital terrain model data cls are inferred from the scaling breaks of the topographic index and curvature distributions and equated with i small scale roughness features and ii the hillslope length scale

quantitative analysis of time lapse seismic monitoring data at the sleipner co2 storage operation the co2 storage operation at sleipner in the norwegian north sea provides an excellent demonstration of the application of time lapse surface seismic methods to co2 plume monitoring under favorable conditions injection commenced at sleipner in 1996 with co2 separated from natural gas being injected into the utsira sand a major saline aquifer of late cenozoic age co2 injection is via a near horizontal well at a depth of about 1012 m below sea level bsl some 200 m below the reservoir top at a rate approaching 1 million tonnes mt per year with more than 11 mt currently stored

geometry and topology of estuary and braided river channel networks automatically extracted from topographic data automatic extraction of channel networks from topography in systems with multiple interconnected channels like braided rivers and estuaries remains a major challenge in hydrology and geomorphology representing channelized systems as networks provides a mathematical framework for analyzing transport and geomorphology in this paper we introduce a mathematically rigorous methodology and software for extracting channel network topology and geometry from digital elevation models dems and analyze such channel networks in estuaries and braided rivers channels are represented as network links while channel confluences and bifurcations are represented as network nodes we analyze and compare dems from the field and those generated by numerical modeling we use a metric called the volume parameter that characterizes the volume of deposited material separating channels to quantify the volume of reworkable sediment deposited between links which is a measure for the spatial scale associated with each network link scale asymmetry is observed in most links downstream of bifurcations indicating geometric asymmetry and bifurcation stability the length of links relative to system size scales with volume parameter value to the power of 0 24 0 35 while the number of links decreases and does not exhibit power law behavior link depth distributions indicate that the estuaries studied tend to organize around a deep main channel that exists at the largest scale while braided rivers have channel depths that are more evenly distributed across scales the methods and results presented establish a benchmark for quantifying the topology and geometry of multichannel networks from dems with a new automatic extraction tool

drainage density and relative relief in humid steep mountains with frequent slope failure previous studies in japanese mountains have shown that drainage density d correlates negatively with relief r and the erosion rate e whereas elsewhere both r and e correlate positively with d to investigate the inconsistency this paper compares two types of d r relations for eight mountain river basins in central japan r is computed from a digital elevation model for 1109 morphometric samples of area 0 5 km 0 5 km drainage networks in these cells were first constructed by map criteria applied previously in japan deeply notched v shaped contours with an angle 53 the resulting d correlates negatively with r confirming preceding studies when drainage lines along shallower hollows were added however the calculated d essentially constant these relations arise from active landsliding in high relief terrains which has eroded steep channel banks into gentle ones the decline of channel banks with increasing r is accelerated in terrains underlain by soft rocks because of rapid erosion the constant d for all the drainage lines indicates a uniform frequency or spacing of ridges and hollows on hillslopes in rugged humid mountains because the d r and d e relations for japan reflect a uniquely japanese physiographic setting characterized by frequent landsliding they differ from those relations for other regions where channelization by gullying predominates 1997 by john wiley sons ltd

high resolution topography for understanding earth surface processes opportunities and challenges abstract in the last decade a range of new remote sensing techniques has led to a dramatic increase in terrain information providing new opportunities for a better understanding of earth surface processes based on geomorphic signatures technologies such as airborne and terrestrial lidar light detection and ranging to obtain high resolution topography have opened avenues for the analysis of landslides hillslope and channellization processes river morphology active tectonics volcanic landforms and anthropogenic signatures on topography this review provides an overview of the recent flourishing literature on high resolution topographic analyses underlining their opportunities and critical issues such as their limitations the goal is to provide answers to questions such as what kind of processes can be analyzed through high resolution topographic data and how to do it the review focuses on two different environments natural and engineered landscapes in both contexts high resolution topography offers opportunities to better understand geomorphic processes from topographic signatures particular attention is given to engineered landscapes in which the direct anthropic alteration of processes is significant the last part of the review discusses future challenges

rapid reactions between co2 brine and silicate minerals during geological carbon storage modelling based on a field co2 injection experiment the dissolution of co2 into formation brines and the subsequent reactions of the co2 charged brines with reservoir minerals are two key processes likely to increase the security of geological carbon dioxide storage these processes will be dependent on the permeability structure and mineral compositions of the reservoirs but there is limited observational data on their rates in this paper we report the cation and anion concentrations and sr oxygen and carbon isotopic compositions of formation waters from four extraction wells sampled at surface over 6 months after commencement of co2 injection in a five spot pattern for enhanced oil recovery at the salt creek field wyoming sampled fluids separated from the minor oil component exhibit near monotonic increases in alkalinity and concentrations of cations but little change in cl and br concentrations and oxygen and deuterium isotope ratios the increases in alkalinity are modelled in terms of reaction with reservoir calcite and silicate minerals as the changes in fluid chemistry and sr isotopic compositions are inconsistent with simple addition of injected fluids sampled over the course of the experiment the reservoir mineral chemical and isotopic compositions are characterised by sampling core as well as surface exposures of the frontier formation elsewhere in wyoming the evolution of the fluid chemistries reflects extensive dissolution of both carbonate and silicate minerals over the course of the six months sampling implying rapid dissolution of co2 in the formation waters and reaction of co2 bearing brines with formation minerals rates of co2 diffusion into the brines and advection of co2 charged brines in the reservoir are sufficiently slow that if present calcite should react to be close to equilibrium with the fluids this allows estimation of the co2 partial pressures in the sampled fluids and comparison with the thermodynamic driving force for the relatively rapid average plagioclase dissolution rates of 10 12 mol m 2 s 1

time lapse tomographic inversion using a gaussian parameterization of the velocity changes most seismic studies of changes in traveltimes are of a qualitative nature and a major challenge in four dimensions is to use the information contained in time shifts to quantify the nature of velocity changes in the subsurface layers we propose a 4d tomographic inversion method that uses time shifts from prestack seismic data to estimate parameters describing the 2d velocity field after changes have occurred prestack data allow for the usage of many offsets thus increasing the information input for the inversion the velocity changes are parameterized by a chosen number of gaussian functions in two dimensions and weighted least squares inversion is used to estimate the parameters describing these functions we have found that the parameters describing the position and shape of the gaussian velocity anomalies can be estimated with this method for simple synthetic cases for more complex cases with overlapping gaussian functions resolution of the parameters can be difficult and in these cases our recom

influence of lithology on hillslope morphology and response to tectonic forcing in the northern sierra nevada of california 1 many geomorphic studies assume that bedrock geology is not a first order control on landscape form in order to isolate drivers of geomorphic change e g climate or tectonics yet underlying geology may influence the efficacy of soil production and sediment transport on hillslopes we performed quantitative analysis of lidar digital terrain models to examine the topographic form of hillslopes in two distinct lithologies in the feather river catchment in northern california a granodiorite pluton and metamorphosed volcanics the two sites separated by 2 km and spanning similar elevations were assumed to have similar climatic histories and are experiencing a transience in landscape evolution characterized by a propagating incision wave in response to accelerated surface uplift c 5 ma responding to increased incision rates hillslopes in granodiorite tend to have morphology similar to model predictions for steady state hillslopes suggesting that they adjust rapidly to keep pace with the incision wave by contrast hillslopes in metavolcanics exhibit high gradients but lower hilltop curvature indicative of ongoing transient adjustment to incision we used existing erosion rate data and the curvature of hilltops proximal to the main channels where hillslopes have most likely adjusted to accelerated erosion rates to demonstrate that the sediment transport coefficient is higher in granodiorite 8 8 m2 ka 1 than in metavolcanics 4 8 m2 ka 1 hillslopes in both lithologies get shorter i e drainage density increases with increasing erosion rates

parameter free delineation of slope units and terrain subdivision of italy abstract quantitative geomorphological and environmental analysis requires the adoption of well defined spatial domains as basic mapping units they provide local boundaries to aggregate environmental and morphometric variables and to perform calculations thus they identify the spatial scale of the analysis grid cells typically aligned with a digital elevation model are the standard mapping unit choice a wiser choice is represented by slope units irregular terrain partitions delimited by drainage and divide lines that maximise geomorphological homogeneity within each unit and geomorphological heterogeneity between neighbouring units adoption of slope units has the advantage of enforcing a strong relation with the underlying topography absent in grid cell based analyses but their objective delineation is still a challenge a given study area admits different slope unit maps differing in number and size of units here we devise an objective optimisation procedure for slope units suitable for study areas of arbitrarily large size and with varying terrain heterogeneity we applied the new approach to the whole of italy resulting in a map containing about 330 000 slope unit polygons of different sizes and shapes the method is parameter free due to objective optimisation using a morphometric segmentation function and the map is readily available for general purpose studies a cluster analysis of slope units properties compared with terrain elevation slope drainage density and lithology confirmed that the terrain partition is geomorphologically sound we suggest the use of the slope unit map for different terrain zonations including landslide susceptibility modelling hydrological and erosion modelling geo environmental ecological forestry agriculture and land use land cover studies requiring the identification of homogeneous terrain domains facing distinct directions

shaping post orogenic landscapes by climate and chemical weathering the spacing of hills and valleys reflects the competition between disturbance driven or diffusive transport on hillslopes and concentrative or advective transport in valleys although the underlying lithologic tectonic and climatic controls have not been untangled here we measure geochemical and geomorphic properties of catchments in kruger national park south africa where granitic lithology and erosion rates are invariant enabling us to evaluate how varying mean annual precipitation map 470 mm 550 mm and 730 mm impacts hill valley spacing or landscape dissection catchment averaged erosion rates based on 10be concentrations in river sands are low 3 6 m m y and vary minimally across the three sites our lidar derived slope area analyses reveal that hillslopes in the dry site are gentle 3 and short such that the terrain is low relief and appears highly dissected with increasing rainfall hillslopes lengthen and increase in gradient 6 8 resulting in less dissected higher relief catchments the chemical depletion fraction of hilltop regoliths increases with rainfall from 0 3 to 0 7 reflecting a climate driven increase in chemical relative to physical erosion soil catenas also vary systematically with climate as we observe relatively uniform soil properties in the dry site that contrast with leached sandy crests and upper slopes coupled with downslope clay accumulation zones in the intermediate and wet sites the geomorphic texture of this slow eroding granitic landscape appears to be set by climate driven feedbacks among chemical weathering regolith fabric differentiation hydrological routing and sediment transport that enhance the vigor of hillslope sediment transport relative to valley forming processes for wetter climates 2013 geological society of america

methane hydrate recycling offshore of mauritania probably after the last glacial maximum to what extent methane liberated from marine hydrate will enter the ocean during a warmer world is unknown although methane release due to hydrate dissociation has been modelled it is unclear whether or not methane will reach the seafloor during a warmer world and therefore contribute to oceanic and atmospheric budgets here we show using a new three dimensional 3 d seismic dataset that some hydrate deposits surround the gas chimneys passing through the hsz bottom water warming since the last glacial maximum lgm is interpreted to cause hydrate dissociation but critically some of the released methane was not vented to the ocean the released gas caused seal failure and free gas entered the hydrate stability zone hsz through vertical gas chimneys to where new hydrate accumulations formed this process is a new evidence for methane recycling and could account in part for the lack of methane in ice core records that cover warming events during the late quaternary this research provides new insight into how methane could be recycled rather than vented during a warmer world

gas generation and overpressure effects on seismic attributes drilling of deep gas resources is hampered by high risk associated with unexpected overpressure zones knowledge of pore pressure using seismic data as for instance from seismic while drilling techniques will help producers plan the drilling process in real time to control potentially dangerous abnormal pressures we assume a simple basin evolution model with a constant sedimentation rate and a constant geothermal gradient oil gas conversion starts at a given depth in a reservoir volume sealed with faults whose permeability is sufficiently low so that the increase in pressure caused by gas generation greatly exceeds the dissipation of pressure by flow assuming a first order kinetic reaction with a reaction rate satisfying the arrhenius equation the oil gas conversion fraction is calculated balancing mass and volume fractions in the pore space yields the excess pore pressure and the fluid saturations this excess pore pressure determines the effective pressure which in turn determines the skeleton bulk moduli if the generated gas goes into solution in the oil this effect does not greatly change the depth and oil gas conversion fraction for which the hydrostatic pressure approaches the lithostatic pressure the seismic velocities versus pore pressure and differential pressure are computed by using a model for wave propagation in a porous medium saturated with oil and gas moreover the velocities and attenuation factors versus frequency are obtained by including rock frame fluid viscoelastic effects to match ultrasonic experimental velocities for the basin evolution model used here pore pressure is seismically visible when the effective pressure is less than about 15 mpa and the oil gas conversion is about 2 5 percent

estimation of rock physics properties from seismic attributes part 1 strategy and sensitivity analysis abstractthe quantitative estimation of rock physics properties is of great importance in any reservoir characterization we have studied the sensitivity of such poroelastic rock physics properties to various seismic viscoelastic attributes velocities quality factors and density because we considered a generalized dynamic poroelastic model our analysis was applicable to most kinds of rocks over a wide range of frequencies the viscoelastic attributes computed by poroelastic forward modeling were used as input to a semiglobal optimization inversion code to estimate poroelastic properties porosity solid frame moduli fluid phase properties and saturation the sensitivity studies that we used showed that it was best to consider an inversion system with enough input data to obtain accurate estimates however simultaneous inversion for the whole set of poroelastic parameters was problematic due to the large number of parameters and their trade off consequently we restricted the sensitivity tests to

bedrock erosion by root fracture and tree throw a coupled biogeomorphic model to explore the humped soil production function and the persistence of hillslope soils 1 in 1877 g k gilbert reasoned that bedrock erosion is maximized under an intermediate soil thickness and declines as soils become thinner or thicker subsequent analyses of this humped functional relationship proposed that thin soils are unstable and that perturbations in soil thickness would lead to runaway thinning or thickening of the soil to explore this issue we developed a numerical model that simulates the physical weathering of bedrock by root fracture and tree throw the coupled biogeomorphic model combines data on conifer population dynamics rootwad volumes tree throw frequency and soil creep from the pacific northwest usa although not hardwired into the model a humped relationship emerges between bedrock erosion and soil thickness the magnitudes of the predicted bedrock erosion rates and their functional dependency on soil thickness are consistent with independent field measurements from a coniferous landscape in the region imposed perturbations of soil erosion during model runs demonstrate that where bedrock weathering is episodic and localized hillslope soils do not exhibit runaway thinning or thickening the pit and mound topography created by tree throw produces an uneven distribution of soil thicknesses across a hillslope thus although episodes of increased erosion can lead to temporary soil thinning and even the exposure of bedrock patches local areas of thick soils remain these soil patches provide habitat for trees and serve as nucleation points for renewed bedrock erosion and soil production model results also suggest that where tree throw is a dominant weathering process the initial mantling of bedrock is not only a vertical process but also a lateral process soil mounds created by tree throw flatten over time spreading soil over bedrock surfaces

leakage from gravity currents in a porous medium part 2 a line sink we consider the propagation of a buoyancy driven gravity current in a porous medium bounded by a horizontal impermeable boundary the current is fed by a constant flux injected at a point and leaks through a line sink at a distance from the injection point this is an idealized model of how a fault in a cap rock might compromise the geological sequestration of carbon dioxide the temporal evolution of the efficiency of storage defined as the instantaneous ratio of the rate at which fluid is stored without leaking to the rate at which it is injected is of particular interest we show that the efficiency of storage decays like t 2 5 for times t that are long compared with the time taken for the current to reach the fault this algebraic decay is in contrast to the case of leakage through a circular sink neufeld et al j fluid mech vol 2010 where the efficiency of storage decays more slowly like 1 ln t the implications of the predicted decay in the efficiency of storage are discussed in the context of geological sequestration of carbon dioxide using parameter values typical of the demonstration project at sleipner norway we show that the efficiency of storage should remain greater than 90 on a time scale of millennia provided that there are no significant faults in the cap rock within about 12 km of the injection site

topographic controls on gravity currents in porous media we present a theoretical and experimental study of the propagation of gravity currents in porous media with variations in the topography over which they flow motivated in part by the sequestration of carbon dioxide in saline aquifers we consider cases where the height of the topography slopes upwards in the direction of the flow and is proportional to the nth power of the horizontal distance from a line or point source of a constant volumetric flux in two dimensional cases with n 1 2 the current evolves from a self similar form at early times when the effects of variations in topography are negligible towards a late time regime that has an approximately horizontal upper surface and whose evolution is dictated entirely by the geometry of the topography for n 0 result in a transition from an early time similarity solution towards a topographically controlled regime that has an approximately horizontal free surface we also analyse the evolution over topography that can vary with different curvatures and topographic exponents between the two horizontal dimensions finding that the flow transitions towards a horizontally topped regime at a rate which depends strongly on the ratio of the curvatures along the principle axes finally we apply our mathematical solutions to the geophysical setting at the sleipner field concluding that topographic influence is unlikely to explain the observed non axisymmetric flow

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

use of the grain size distribution for estimation of the soil water characteristic curve the implementation of unsaturated soil mechanics into engineering practice is dependent to a large extent upon an ability to estimate unsaturated soil property functions the soil water characteristic curve swcc along with the saturated soil properties has proven to provide a satisfactory basis for estimating the permeability function and shear strength functions for an unsaturated soil the volume change functions have not been totally defined nor applied in geotechnical engineering the objective of this paper is to present a procedure for estimating the swcc from information on the grain size distribution and the volume mass properties of a soil swccs represent a continuous water content versus soil suction relationship the proposed method provides an approximate means of estimating the desorption curve corresponding to a soil initially slurried near the liquid limit the effects of stress history fabric confining pressure and hysteresis are not addressed a database of published data is use

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

fluid transport in geological reservoirs with background flow this paper presents fundamental analysis of the injection and release of fluid into porous media or geological reservoirs saturated by a different fluid undergoing a background flow and tests the predictions using analogue laboratory experiments the study reveals new results important for an understanding of the transport of hazardous contaminants through aquifers and the long term fate of carbon dioxide in geological sequestration using numerical and asymptotic analysis we describe a variety of flow regimes that arise and demonstrate an almost instantaneous control of injected fluid by the far field conditions in geological reservoirs for a continuous input the flow develops a horizontal interface between the injected and ambient fluids the background flow thereby effectively caps the height of the injected fluid into a shallower region of vertical confinement for a released parcel of fluid gravitational spreading is found to become negligible after a short time a dominant control of the interface by the background pressure gradient arises and stems from the different velocities at which it drives the injected and ambient fluids individually similarity solutions describing these dynamics show that the parcel approaches a slender triangular profile that grows horizontally as where is time a rate faster than relaxation under gravity shock layers develop at the front or back of the parcel depending on whether it is more or less viscous than the ambient fluid new analytical results describing the long term effects of residual trapping due to capillary retention are developed which yield explicit predictions for the time and length scales on which a parcel of becomes retained we end by applying our results to geological contexts concluding that even slight background motion can have considerable implications for long term transport through the subsurface

dual sensor streamer technology used in sleipner co2 injection monitoring co2 has been injected into the saline aquifer utsira fm at the sleipner field since 1996 in order to monitor the movement of the co2 in the sub surface the seventh seismic monitor survey was acquired in 2010 with dual sensor streamers which enabled optimal towing depths compared to previous surveys we here report both on the time lapse observations and on the improved resolution compared to the conventional streamer surveys this study shows that the co2 is still contained in the subsurface with no indications of leakage the time lapse repeatability of the dual sensor streamer data versus conventional data is sufficient for interpreting the timelapse effects of the co2 at sleipner and the higher resolution of the 2010 survey has enabled a refinement of the interpretation of nine co2 saturated layers with improved thickness estimates of the layers in particular we have estimated the thickness of the uppermost co2 layer based on an analysis of amplitude strength together with time separation of top and base of this layer and found the maximum thickness to be 11 m this refined interpretation gives a good base line for future time lapse surveys at the sleipner co2 injection site

localizing co2 at sleipner seismic images versus p wave velocities from waveform inversion abstractthe presence of injected co2 in the utsira sand at the sleipner site norway is associated with a high negative p wave velocity anomaly that is a low postinjection velocity and a strong seismic response time lapse seismic imaging of co2 injection at sleipner is thus a viable monitoring tool of the injected co2 the work flow usually involves conventional seismic processing including stacking and results in seismic images multiple reflections interference effects such as tuning and the velocity pushdown effect due to co2 injection render these seismic images ambiguous in terms of the localization and the quantification of the co2 in the utsira sand nonetheless seismic images often form the basis for analyses that aim to quantify the injected co2 we employed elastic 2d full waveform inversion to invert prestack seismic sleipner data from preinjection 1994 and postinjection 1999 and compared the resulting postinjection p wave velocity model with the corresponding seismic image we fou

palynological and foraminiferal biostratigraphy of upper pliocene nordland group mudstones at sleipner northern north sea abstract the nordland group is an important stratigraphical unit within the upper cenozoic of the northern north sea at its base lies the utsira sand a dominantly sandy regional saline aquifer that is currently being utilized for carbon dioxide sequestration from the sleipner gas and condensate field a mudstone drape immediately overlies the utsira sand forming the caprock for this aquifer the upper part of the utsira sand was recently dated as early pliocene but the precise age of the overlying nordland group mudstones has remained uncertain dinoflagellate cyst pollen and spore foraminiferal and stable isotopic analyses have been performed on these mudstones from a conventional core within the interval 913 10 906 00 m drilled depth in norwegian sector well 15 9 a 11 the samples lie closely above the utsira sand results give a gelasian late late pliocene age for this interval with a planktonic foraminiferal assemblage at 913 10 m indicating warm climatic conditions and an age between 2 4 and 1 8 ma an abundance of the cool tolerant dinoflagellate cysts filisphaera filifera and habibacysta tectata at 906 00 m along with evidence from pollen and foraminifera points to deposition during a cool phase of the gelasian dating the mudstone drape provides useful insights into depositional processes it seems likely that the utsira sand a basinal lowstand deposit became progressively starved of clastic input as sea level rose and shorelines retreated the mudstone drape is interpreted as a highstand deposit perhaps including a maximum flooding surface overlying prograding wedges of the nordland group form a regressive succession characterized by increased sedimentary input and rates of deposition of at least 25 cm per 1000 years which is more than five times that of the utsira sand this is the first published study of a dinoflagellate cyst assemblage from the upper pliocene of the northern north sea the new dinoflagellate cyst species echinidinium nordlandensis head sp nov and echinidinium sleipnerensis head riding sp nov are formally described

bounds on low frequency seismic velocities in partially saturated rocks the most common technique for estimating seismic velocities in rocks with mixed pore fluid saturations is to use gassmann s relations with an effective fluid whose density and compressibility are averages of the individual pore fluid properties this approach is applicable only if the gas oil and brine phases are mixed uniformly at a very small scale so the different wave induced increments of pore pressure in each phase have time to diffuse and equilibrate during a seismic period in contrast saturations that are heterogeneous over scales larger than the characteristic diffusion length i e patchy saturation will always lead to higher seismic velocities than if the same fluids are mixed uniformly at a fine scale critical saturation scales separating uniform from patchy behavior are typically of the order 0 1 1 cm for laboratory measurements and tens of centimeters for field seismic frequencies for low seismic frequencies velocities corresponding to patchy and homogeneous saturations represent a

the seismic response to overpressure a modelling study based on laboratory well and seismic data we investigate the seismic detectability of an overpressured reservoir in the north sea by computing synthetic seismograms for different pore pressure conditions the modelling procedure requires the construction of a geological model from seismic well and laboratory data seismic inversion and avo techniques are used to obtain the p wave velocity with higher reliability than conventional velocity analysis from laboratory experiments we obtain the wave velocities of the reservoir units versus confining and pore pressures laboratory experiments yield an estimate of the relationship between wave velocities and effective pressure under in situ conditions these measurements provide the basis for calibrating the pressure model overpressures are caused by different mechanisms we do not consider processes such as gas generation and diagenesis which imply changes in phase composition but focus on the effects of pure pore pressure variations the results indicate that changes in pore pressure can be detected with seismic methods under circumstances such as those of moderately deep north sea reservoirs