the impact of airmass boundaries on the propagation of deep convection a modeling based study in a high cape low shear environment a suite of experiments conducted using a cloud resolving model is examined to assess the role that preexistingairmassboundariescanplayinregulatingstormpropagation the27may1997centraltexastornadic event is used to guide these experiments the environment of this event was characterized by multiple preexisting airmass boundaries large cape and weak vertical shear only the experiments with preexisting airmass boundaries produce back building storm propagation storm motion in opposition to the mean wind when both the cold front and dryline are present storm maintenance occursthroughthe quasi continuousmaintenance ofa setoflong livedupdraftsandnotthrough discrete updraft redevelopment since the cold front is not required for back building it is clear that back building in this environment does not require quasi continuous updraft maintenance the back building storm simulated with both the cold front and dryline is found to be anchored to the boundary zipper the intersection of the cold front and dryline however multiplepreexisting airmass boundaries are not required for back building since experiments with only a dryline also support back building a conceptual model of back building and boundary zippering is developed that highlights the important role that preexisting boundaries can play in back building propagation

osmotic generation of anomalous fluid pressures in geological environments osmotic pressures are generated by differences in chemical potential of a solution across a membrane but whether osmosis can have a significant effect on the pressure of fluids in geological environments has been controversial because the membrane properties of geological media are poorly understood anomalous pressures large departures from hydrostatic pressure that are not explicable in terms of topographic or fluid density effects are widely found in geological settings and are commonly considered to result from processes that alter the pore or fluid volume which in turn implies crustal changes happening at a rate too slow to observe directly yet if osmosis can explain some anomalies there is no need to invoke such dynamic geological processes in those cases here i report results of a nine year in situ measurement of fluid pressures and solute concentrations in shale that are consistent with the generation of large up to 20 mpa osmotic pressure anomalies which could persist for tens of millions of years osmotic pressures of this magnitude and duration can explain many of the pressure anomalies observed in geological settings they require however small shale porosity and large contrasts in the amount of dissolved solids in the pore waters criteria that may help to distinguish between osmotic and crustal dynamic origins of anomalous pressures

relationship between a weakening cold front misocyclones and cloud development on 10 june 2002 during ihop abstract the finescale structure and evolution of a cold front in the presence of small scale circulations are examined using overdetermined dual doppler syntheses of mobile radar data along with thermodynamic data and cloud imagery collected on 10 june 2002 during the international h2o project ihop linear clear air reflectivity maxima and open cellular convection intersect the cold front causing spatial variations in convergence along the front small scale vertical vorticity maxima misocyclones often are coincident with these intersections and are associated with vertical velocity maxima throughout the deployment trajectory analyses indicate that parcels entering the frontal circulation travel predominately in the along front direction during the first hour of the deployment upward motion is nearly continuous along the front consequently parcels remain in regions of upward motion as they move along the front and many eventually ascend to cloud base in response a line of cumulus clouds dev

a procedure for landslide susceptibility zonation by the conditional analysis method numerous methods have been proposed for landslide probability zonation of the landscape by means of a geographic information system gis among the multivariate methods i e those methods which simultaneously take into account all the factors contributing to instability the conditional analysis method applied to a subdivision of the territory into unique condition units is particularly straightforward from a conceptual point of view and particularly suited to the use of a gis in fact working on the principle that future landslides are more likely to occur under those conditions which led to past instability landslide susceptibility is defined by computing the landslide density in correspondence with different combinations of instability factors the conceptual simplicity of this method however does not necessarily imply that it is simple to implement especially as it requires rather complex operations and a high number of gis commands moreover there is the possibility that in order to achieve satisfactory results the procedure has to be repeated a few times changing the factors or modifying the class subdivision to solve this problem we created a shell program which by combining the shell commands the gis geographical research analysis support system grass commands and the gawk language commands carries out the whole procedure automatically this makes the construction of a landslide susceptibility map easy and fast for large areas too and even when a high spatial resolution is adopted as shown by application of the procedure to the parma river basin in the italian northern apennines

a country wide spatial assessment of landslide susceptibility in romania abstract this paper proposes a brief spatial analysis of landslides in romania completed by a landslide susceptibility model landslides constitute a very common geomorphic hazard in this country mainly in the hilly regions which occupy around 30 of romania s territory the landslide susceptibility assessment at national level was accomplished using a landslide susceptibility index lsi computed in gis which considers and weights the main factors that control landslide activity lithology slope gradient maximum rainfall in 24 h land use seismicity and local relief each factor was classified into 7 18 classes which were rated from 1 to 10 by means of expert judgement a formula was devised to compute the landslide susceptibility index over each 100 m 100 m pixel and the resulting values were ranked into 5 landslide susceptibility classes this synthetic method of landslide susceptibility assessment applied to the whole country is a useful tool to evaluate the distribution of landslide prone areas as well as to validate and to enhance some results obtained in previous studies based on field research and map interpretation the most landslide prone areas correspond to the subcarpathians an outer fringe of hilly terrain accompanying the carpathians as well as to the moldavian plateau in the east the semi quantitative approach has been validated with satisfactory results in a particular sector using independent cartographic landslide inventories

osmotic model to explain anomalous hydraulic heads laboratory experiments have shown that compacted clays act as osmotic membranes when they separate aqueous solutions of unequal ionic concentration theoretically osmotically induced differential hydraulic pressure in groundwater systems can be relatively high the magnitude depends primarily upon concentration differences across the membrane type of ions type of clay and pore size in experiments thin compacted clay membranes commonly exhibit varying degrees of osmotic efficiency due to ion leak age through the clay in natural systems the membrane and the solution containers are not as distinct and well defined as they are in the laboratory moreover the membrane is commonly thick inhomogeneous and composite in a buried triassic basin at the savannah river plant near aiken south carolina it is suspected that osmosis causes the saline water in the basin center to be slightly geopressurized in relation to freshwater in the overlying coastal plain aquifer two wells have heads of 7 88 and 12 98 bars 114 3 and 188 3 psi above the head in the coastal plain aquifer the head in each of these wells approximates the osmotic equilibrium head calculated from solution concentration of water produced by each well 12 000 and 18 500 mg l respectively other wells penetrating the top and edge of the triassic basin probably penetrate a zone where ion leakage gives rise to less saline water thus these wells are not geopressurized

use of vertical profiles of δ18o to constrain estimates of hydraulic conductivity in a thick unfractured aquitard vertical distributions of 18o were used to constrain hydraulic conductivity k in a thick unfractured aquitard previous investigations utilizing permeability tests at a variety of scales keller et al 1989 indicated that bulk k at the site ranges from 3 5 0 11 m s to 1 2 10 10 m s advective displacements calculated on the basis of these k values lead to a wide range of predicted distributions of natural tracers after 11 000 years comparison of 18o distributions and simulated advection diffusion profiles provide a more precise constraint on advective displacement and hence on k the simulations cast in terms of a peclet number p v2t d ranging in value from 0 to 12 indicate that transport is diffusion controlled and that k is actually less than 1 2 10 11 m s p greater than 0 1 k 1 2 10 11 m s overestimates transport this result indicates that conventional permeability tests in very tight media tend to overestimate k in practical terms advective transport at the site is negligible and transport can be simulated with diffusion only p o

a gis based approach for gully erosion susceptibility modelling a test in sicily italy the aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the magazzolo river basin and to test a method that allows for driving the factors selection the study area is one of the largest 225 km2 watershed of southern sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments except for the northern sector where carbonatic rocks give rise to steep slopes in order to obtain a quantitative evaluation of gully erosion susceptibility statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed stereoscopic analysis of aerial photographs dated 2000 and field surveys carried out in 2006 allowed us to map about a thousand landforms produced by linear water erosion processes classifiable as ephemeral and permanent gullies the linear density of the gullies computed on each of the factors classes was assumed as the function expressing the susceptibility level of the latter a 40 m digital elevation model dem prepared from 1 10 000 scale topographic maps was used to compute the values of nine topographic attributes primary slope aspect plan curvature profile curvature general curvature tangential curvature secondary stream power index topographic wetness index ls usle factor from available thematic maps and field checks three other physical attributes lithology soil texture land use were derived for each of these variables a 40 m grid layer was generated reclassifying the topographic variables according to their standard deviation values in order to evaluate the controlling role of the selected predictive variables one variable susceptibility models based on the spatial relationships between each single factor and gullies were produced and submitted to a validation procedure the latter was carried out by evaluating the predictive performance of models trained on one half of the landform archive and tested on the other large differences of accuracy were verified by computing geometric indexes of the validation curves prediction and success rate curves roc curves drawn for each one variable model in particular soil texture general curvature and aspect demonstrated a weak or a null influence on the spatial distribution of gullies within the studied area while on the contrary tangential curvature stream power index and plan curvature showed high predictive skills hence predictive models were produced on a multi variable basis by variously combining the one variable models the validation of the multi variables models which generally indicated quite satisfactory results were used as a sensitivity analysis tool to evaluate differences in the prediction results produced by changing the set of combined physical attributes the sensitivity analysis pointed out that by increasing the number of combined environmental variables an improvement of the susceptibility assessment is produced this is true with the exception of adding to the multi variables models a variable as slope aspect not correlated to the target variable the addition of this attribute produces effects on the validation curves that are not distinguishable from noise and as a consequence the slope aspect was excluded from the final multi variables model used to draw the gully erosion susceptibility map of the magazzolo river basin in conclusion the research showed that the validation of one variable models can be used as a tool for selecting factors to be combined to prepare the best performing multi variables gully erosion susceptibility model

the 8 june 1995 mclean texas storm part i observations of cyclic tornadogenesis abstract on 8 june 1995 scientists participating in the verification of the origins of rotation in tornadoes experiment vortex collected airborne doppler radar data in a storm that produced a family of tornadoes near mclean texas the electra doppler radar eldora scanned three significant tornadoes during their formative and mature stages one of the tornadoes was of f4 f5 intensity evidence from pseudo dual doppler analyses of the eldora data reveals a process of cyclic tornado formation qualitatively similar to that depicted in previous conceptual models in particular the rear flank gust front appears to play a major role in determining the location of the next vortex in the series when a tornado forms a small region 3 5 km wide of outflow surges ahead of the tornado producing a local bulge in the gust front a new vorticity maximum may form near the leading edge of the outflow in contrast to what is suggested by earlier conceptual models intersection of the rear flank gust front with a w

frequency ratio model based landslide susceptibility mapping in lower mae chaem watershed northern thailand the purpose of this study is to produce a landslide susceptibility map for the lower mae chaem watershed northern thailand using a geographic information system gis and remotely sensed images for this purpose past landslide locations were identified from satellite images and aerial photographs accompanied by the field surveys to create a landslide inventory map ten landslide inducing factors were used in the susceptibility analysis elevation slope angle slope aspect lithology distance from lineament distance from drainage precipitation soil texture land use land cover lulc and ndvi the first eight factors were prepared from their associated database while lulc and ndvi maps were generated from landsat 5 tm images landslide susceptibility was analyzed and mapped using the frequency ratio fr model that determines the level of correlation between locations of past landslides and the chosen factors and describes it in terms of frequency ratio index finally the output map was validated using the area under the curve auc method where the success rate of 80 06 and the prediction rate of 84 82 were achieved the obtained map can be used to reduce landslide hazard and assist with proper planning of lulc in the future

multiscale aspects of thunderstorm gust fronts and their effects on subsequent storm development abstract an investigation of severe storms that occurred on 23 may 1974 in central oklahoma reveals interesting information on the multifaceted role of thunderstorm produced gust fronts the data reveal that the interaction of outflow boundaries with a cold front initiate the storms studied in this report then the gust fronts produced by these storms have important effects on their own structure and life histories detailed doppler analysis show that these storms propagate discretely along their outflow boundaries despite their supercell structure additionally one storm is affected by its interaction with the boundary produced by a previous storm this interaction appears responsible for tornadogenesis

the role of forcing in cell morphology and evolution within midlatitude squall lines abstract this study assesses the role of mesoscale forcing on cell morphology and early evolution of midlatitude squall lines the forcing chosen was a cold front simulated to frontal collapse to produce a specific set of thermodynamic profiles at the leading edge of the front use of a realistic balanced and persistent forced state allowed a unique evaluation of its importance in thunderstorm evolution compared with a traditional homogeneous environment without forcing three dimensional squall lines were modeled with and without the front present in low and high bulk richardson number environments the forced convection evolved in significantly different ways than their isolated unforced counterparts in low shear conditions the line of isolated convective cells split with the adjacent split cells interfering destructively with neighboring cells in the line with forcing present differences in anticyclonic cell intensity and propagation prevented this interaction from occurring leading to longe

hydraulic and chemical pulse tests in a shut in chamber imbedded in an argillaceous formation numerical and experimental approaches hydraulic and chemical pulse tests were performed in four shut in chambers to obtain hydraulic and chemical parameters of the callovo oxfordian shale the osmotic tests i e chemical pulses were carried out by exchange of the formation water for a different solution either more or less concentrated two sets of two osmotic tests were done in march and october 2006 these osmotic tests are superimposed on a purely hydraulic response because of the drilling of the well causing a pressure drop the pressure records hydraulic and osmotic responses were interpreted using a 2 d model to obtain the hydraulic and chemical parameters the osmotic efficiency inferred for the callovo oxfordian shale is on the order of 0 012 for a concentration of 0 43 mol l 1 and 0 12 for a concentration of 0 086 mol l 1 these results suggest that the callovo oxfordian shale behaves as a weakly semipermeable membrane and only 0 1 0 15 mpa of the 0 2 0 5 mpa can be explained by these osmotic efficiency values

landslide hazard assessment of the 2008 wenchuan earthquake a case study in beichuan area the wenchuan earthquake magnitude ms 8 0 of 12 may 2008 triggered widespread and large scale landslides over an area of about 50 000 km2 a study was undertaken to determine the primary factors associated with seismic landslide occurrence an index based approach used to assess earthquake triggered landslide hazard in the central part of the wenchuan earthquake area affected is described slope gradient relief amplitude lithology bedding slope relations fault proximity stream proximity and antecedent rainfall are recognized as factors that may have had an important influence on landslide occurrence the assessment of the influence of each of these factors is presented through use of a series of maps showing areas of low moderate high and very high landslide hazard areas identified as having very high and high landslide hazard were located along the earthquake source fault and along both banks of the jian river the role of rainfall is very significant for future landslide occurrence in the

experimental support for a predictive osmotic model of clay membranes osmosis has been cited as a mechanism for explaining anomalously high fluid pressures in the subsurface clays and shales act as membranes and osmotic flux across these units may result in pressures sufficiently high to explain these anomalies the theoretical osmotic pressures as calculated solely from solution properties can be quite large however it is not yet resolved whether these geologic membranes are sufficiently ideal to generate such pressures

landslide susceptibility assessment by bivariate methods at large scales application to a complex mountainous environment statistical assessment of landslide susceptibility has become a major topic of research in the last decade most progress has been accomplished on producing susceptibility maps at meso scales 1 50 000 1 25 000 at 1 10 000 scale which is the scale of production of most regulatory landslide hazard and risk maps in europe few tests on the performance of these methods have been performed this paper presents a procedure to identify the best variables for landslide susceptibility assessment through a bivariate technique weights of evidence woe and discusses the best way to minimize conditional independence ci between the predictive variables indeed violating ci can severely bias the simulated maps by over or under estimating landslide probabilities the proposed strategy includes four steps i identification of the best response variable rv to represent landslide events ii identification of the best combination of predictive variables pvs and neo predictive variables npvs to increase the performance of the statistical model iii evaluation of the performance of the simulations by appropriate tests and iv evaluation of the statistical model by expert judgment the study site is the north facing hillslope of the barcelonnette basin france affected by several types of landslides and characterized by a complex morphology results indicate that bivariate methods are powerful to assess landslide susceptibility at 1 10 000 scale however the method is limited from a geomorphological viewpoint when rvs and pvs are complex or poorly informative it is demonstrated that expert knowledge has still to be introduced in statistical models to produce reliable landslide susceptibility maps

a slug test to assess the osmotic and hydraulic properties of argillaceous formations pulse tests in pressurized chambers represent a very efficient method to estimate the hydrodynamic properties of low permeability formations useful analytical solutions for purely hydraulic pulse test interpretation have been proposed in the present note an extension of the classical model by bredehoeft and papadopulos 1980 is developed for a single hydraulic and or chemical osmotic pulse test involving laplace transforms this solution is used to identify graphical variables in an osmotic pulse test record which can be used to estimate the relevant hydrochemical parameters

landslide hazard evaluation a review of current techniques and their application in a multi scale study central italy in recent years growing population and expansion of settlements and life lines over hazardous areas have largely increased the impact of natural disasters both in industrialized and developing countries third world countries have difficulty meeting the high costs of controlling natural hazards through major engineering works and rational land use planning industrialized societies are increasingly reluctant to invest money in structural measures that can reduce natural risks hence the new issue is to implement warning systems and land utilization regulations aimed at minimizing the loss of lives and property without investing in long term costly projects of ground stabilization government and research institutions worldwide have long attempted to assess landslide hazard and risks and to portray its spatial distribution in maps several different methods for assessing landslide hazard were proposed or implemented the reliability of these maps and the criteria behind these hazard evaluations are ill formalized or poorly documented geomorphological information remains largely descriptive and subjective it is hence somewhat unsuitable to engineers policy makers or developers when planning land resources and mitigating the effects of geological hazards in the umbria and marche regions of central italy attempts at testing the proficiency and limitations of multivariate statistical techniques and of different methodologies for dividing the territory into suitable areas for landslide hazard assessment have been completed or are in progress at various scales these experiments showed that despite the operational and conceptual limitations landslide hazard assessment may indeed constitute a suitable cost effective aid to land use planning within this framework engineering geomorphology may play a renewed role in assessing areas at high landslide hazard and helping mitigate the associated risk

susceptibility assessments of shallow earthflows triggered by heavy rainfall at three catchments by logistic regression analyses abstract sometimes regional meteorological anomalies trigger different types of mass movements in may 1998 the western black sea region of turkey experienced such a meteorological anomaly numerous residential and agricultural areas and engineering lifelines were buried under the flood waters besides the reactivation of many previously delineated landslides thousands of small scale landslides mostly the earthflow type occurred all over the region the earthflows were mainly developed in flysch type units which have already presented high landslide concentrations in this study three different catchments namely agustu egerci and kelemen were selected because they have the most landslide prone geological units of the region the purposes of the present study are to put forward the spatial distributions of the shallow earthflows triggered to describe the possible factors conditioning the earthflows and to produce the shallow earthflow susceptibility maps of the three catchments the unique condition units ucu were employed during the production of susceptibility maps and during statistical analyses the unique condition units numbered 4052 for the agustu catchment 13 241 for the egerci catchment and 12 314 for the kelemen catchment the earthflow intensity is the highest in the agustu catchment 0 038 flow ucu and lowest in the egerci catchment 0 0035 flow ucu logistic regression analyses were also employed however during the analyses some difficulties were encountered to overcome the difficulties a series of sensitivity analyses were performed based on some decision rules introduced in the present study considering the decision rules the proper ratios of ucu free from earthflow 0 ucu including the earthflow 1 for the agustu egerci and kelemen catchments were obtained as 3 6 and 5 respectively also a chart for the proper ratio selection was developed the regression equations from the selected ratios were then applied to the entire catchment and the earthflow susceptibility maps were produced the landslide susceptibility maps revealed that 15 of the agustu catchment 8 of the egerci catchment and 7 of the kelemen catchment have very high earthflow susceptibility and most of the earthflows triggered by the may 1998 meteorological event were found in the very high susceptibility zones

analytical and numerical solutions for alternative overpressuring processes application to the callovo oxfordian sedimentary sequence in the paris basin france 1 previous studies that made use of basin models have shown that the normal geological evolution of the paris basin does not generate the observed albeit weak excess pressures in some shale layers of the basin other processes that may have created the overpressures currently neglected in such models are investigated here terms accounting for osmotic effects and tectonic stress changes are successively added to the diffusivity equation the effect of changes in outcrop boundary conditions is also calculated with a pseudo two dimensional analytical solution these solutions are applied to the callovo oxfordian shale formation in the eastern part of the paris basin france it is shown that a long term transient osmotic effect starting in the tertiary could explain in part the observed excess pressures in the callovo oxfordian shale assuming effective diffusion coefficients of 1 5 10 12 m2 s 1 in line with the measurements and a pore radius b around 20 a for the shales however because of the uncertainty on the value of the shale pore radius additional head measurements and osmotic experiments on samples should be made to fully establish the possibility of an osmotic process our study also shows that recent changes in hydrodynamic boundary conditions could also explain excess pressure distribution in this shale layer it is plausible that a combination of the two processes could best explain the distribution and intensity of the overpressures tectonic stress changes do not appear to be important it is shown that for such processes to maintain high pressures strong and recent increase in tectonic compressive stress would be required

stress field determinations in france by hydraulic tests in boreholes the stress field has been determined at eight different sites in france four in crystalline or metamorphic rocks four in sedimentary formations by hydraulic tests in boreholes for seven of these sites the complete stress field has been determined using the hydraulic tests on pre existing fractures htpf inversion method validity of the results is demonstrated by the good fit between a priori and a posteriori values for the data and by the low values of the a posteriori standard deviation on the unknowns for four sites results have been compared with those derived according to the hydraulic fracturing theory the two methods yield comparable results for the orientation of the maximum horizontal principal stress h a generally satisfactory fit for the magnitude of the minimum horizontal principal stress h but a very poor agreement for the magnitude of h this latter misfit has been attributed to the effect of fluid percolation prior to the actual opening of the fractures below a depth of 500 m a homogeneous h direction n150 e has been determined at the crystalline sites auriat echassieres le mayet de montagne chassoles all located in the northern massif central for three of these sites the vertical stress is significantly lower than the weight of overburden as computed from the rock density and the depth of the corresponding measurement at auriat and echassieres the stress field is consistent with a mostly strike slip faulting regime at le mayet de montagne and chassoles the maximum stress is vertical but nearly equal to h the stress field has been found to be much more heterogeneous at two of the four sites in sedimentary rocks because of the large variability in mechanical rock properties in such heterogeneous formations inversion with the htpf method must be limited to those data which pertain to the same rock horizon however because of its structure this heterogeneity does not restrict the possibility of defining large scale uniform principal stress directions all the results are consistent with the local seismotectonics

the motion of simulated convective storms as a function of basic environmental parameters abstract based on results from a three dimensional cloud resolving model it is shown that simulated convective storm motions are affected by thermodynamic as well as kinematic properties of the environment in addition to the mean wind and its vertical shear the effect on isolated storm motion of parameters such as bulk convective available potential energy cape the vertical distribution of buoyancy in the profile the heights of the lifting condensation level lcl and level of free convection lfc and cloud base temperature is considered storm motions show at least some sensitivity to all input parameters consistent with previous studies hodograph radius has the most pronounced effect but the vertical distribution of shear which also influences the mean wind affects storm evolution and propagation even when the effective hodograph radius is unchanged among the thermodynamic parameters the most significant variations occur when the lcl lfc configuration is modified or when cloud base temp

interactions between a supercell and a quasi stationary frontal boundary abstract the case presented here is submitted as an example of a previously undocumented type of interaction between a supercell thunderstorm and a frontal boundary during the afternoon of 8 june 1995 a supercell thunderstorm formed near a quasi stationary frontal boundary and then moved northeast across beaver county in the oklahoma panhandle its motion took it away from the boundary and deeper into the cool air as the storm matured and strengthened a portion of the boundary to the south of the supercell moved northward and briefly became entrained in the low level circulation of the storm this northward advance of the boundary was subsequently followed by a southward motion back to near its original location high density spatial and temporal observations from the oklahoma mesonet and the verification of the origins of rotation in tornadoes experiment vortex mobile mesonetwork are presented to document the northward advance of the boundary into the supercell circulation

time to reach near steady state in large aquifers 1 a new analytical solution of the flow equation has been developed to estimate the time to reach a near equilibrium state in mixed aquifers i e having unconfined and confined portions following a large hydraulic perturbation near equilibrium is defined as the time for an initial aquifer perturbation to dissipate by an average 95 across the aquifer the new solution has been obtained by solving the flow system of a simplified conceptual model of a mixed aquifer using laplace transforms the conceptual model is based on two assumptions 1 the groundwater flow can be reduced to a horizontal 1 d problem and 2 the transmissivity a function of the saturated thickness is assumed constant on the unconfined portion this new solution depends on the storativity of the unconfined portion the lengths of the unconfined and confined portions and the transmissivity assumed to be constant and equal in both portions of the mixed aquifer this solution was then tested and validated against a numerical flow model where the variations of the saturated thickness and therefore variations of the transmissivity were either ignored or properly modeled the agreement between the results from the new solution and those from the numerical model is good validating the use of this new solution to estimate the time to reach near equilibrium in mixed aquifers this solution for mixed aquifers as well as the solutions for a fully confined or fully unconfined aquifer has been used to estimate the time to reach near equilibrium in 13 large aquifers in the world for those different aquifers the time to reach near equilibrium ranges between 0 7 kyr to 2 4 107 kyr these results suggest that the present hydraulic heads in these aquifers are typically a mixture of responses induced from current and past hydrologic conditions and thus climate conditions for some aquifers the modern hydraulic heads may in fact depend upon hydrologic conditions resulting from several past climate cycles

flow of variable density formation water in deep sloping aquifers review of methods of representation with case studies abstract distributions of freshwater hydraulic heads have been and continue to be used in the representation and analysis of groundwater flow including the flow of variable properties formation water in deep sloping aquifers because of variations in pressure temperature and salinity the flow of formation waters in sedimentary basins is driven by potential forces resulting from pressure and elevation topography differences by buoyancy resulting from density differences and by osmosis caused by temperature and concentration gradients because of variations in both fluid and rock properties it is not possible to define a flow potential to be used in representing and analysing the flow neither is there a force potential from which a flow driving force can be derived and which could be used in flow representation and analysis even if osmotic effects are neglected buoyancy still plays a role which in certain cases may be important in horizontal or near horizontal aquifers the lateral flow of variable density water is correctly represented by freshwater potentiometric surfaces and the vertical flow may be analysed using environmental hydraulic head distributions however the flow of formation waters in sedimentary basins is mostly along bedding in confined sloping aquifers in this case short of calculating and representing either the velocity or the impelling force distribution freshwater hydraulic heads remain the only tool available for representing and analysing the flow by neglecting buoyancy errors in flow strength and direction are introduced which become significant if a dimensionless driving force ratio exceeds a threshold value estimated to be around 0 5 the review of representation and analysis methods for the flow of variable properties formation water in deep sloping aquifers is illustrated with two case studies from the alberta and llanos sedimentary basins

bayesian inversion of a chloride profile obtained in the hydraulically undisturbed opalinus clay mass transport and paleo hydrological implications abstract the bdb 1 deep inclined borehole was drilled at the mont terri rock laboratory switzerland and enabled to acquire relevant data on porewater composition through the opalinus clay opa and its bounding formations petrophysical measurements were carried out and included water content water accessible porosity and grain density determination conservative anion profiles were obtained by aqueous leaching and out diffusion experiments performed on drillcore samples and revealed to be consistent with previous studies carried out at the rock laboratory level diffusive properties were also investigated using three experimental setups cubic out diffusion radial diffusion and through diffusion these transport parameters were used as a priori values in a bayesian inversion using a markov chain monte carlo method to interpret the chloride profile in the opalinus clay based on a peclet number analysis using the transport parameters formerly acquired a purely diffusive scenario enabled specifying the paleohydrogeological evolution of the mont terri site from the folding and thrusting of the jura mountains to present time and transport parameters

variability of storm relative helicity during vortex in this paper storm relative helicity srh and low level vertical shear of the horizontal wind fields were investigated on the mesoscale and stormscale in regions where tornadoes occurred for four case studies using data collected during the verification of the origin of rotation in tornadoes experiment a primary finding was that srh was highly variable in both time and space in all of the cases suggesting that this parameter might be difficult to use to predict which storms might become tornadic given the available national weather service upper air wind data second it was also found that the shear between the lowest mean 500 m wind and the 6 km wind was fairly uniform over vast regions in all of the four cases studied thus this parameter provided little guidance other than that there was possibly enough shear to support supercells it was contended that forecasters will need to monitor low level features such as boundaries or wind accelerations which might augment streamwise vorticity ingested into storms finally it was suggested that one reason why one storm might produce a tornado while a nearby one does not might be due to the large variations in srh on very small spatial and temporal scales in other words only those storms that move into regions small or large with sufficient srh might produce tornadoes

importance of thermo osmosis for fluid flow and transport in clay formations hosting a nuclear waste repository abstract three osmotic processes have been identified in clay rich media electro and chemo osmosis flows of water caused by salinity and electrical potential gradients have so far attracted almost exclusive attention but despite the recurring concern about the importance of thermo osmosis a flow of water driven by a temperature gradient in argillaceous media it remains largely neglected here we propose a new formalism for estimating the thermo osmotic permeability based on a theoretical analysis at the molecular and pore scale then upscaled we show that the thermo osmotic permeability can be estimated only from surface charge density temperature pore size and salinity the possible prominent role of thermo osmosis in compacted shale layers with a temperature gradient is then exemplified this first general estimate of the thermo osmotic permeability can be used to improve our understanding of the influence on fluid flow and pressure fields of the natural geothermal gradient in sedimentary basins which is required e g for safety assessments of nuclear waste repositories in shale layers

chlorine transfer out of a very low permeability clay sequence paris basin france 35cl and 37cl evidence abstract the marine callovo oxfordian clay formation is found at a depth around 410m in the eastern part of the paris basin france it is a very low permeability formation investigated by the french agency for nuclear waste management andra to study the feasibility of a radioactive waste disposal examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation this study uses chlorine isotopes to investigate long term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks detailed chlorine concentration and 37cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers the dogger at the bottom and the oxfordian kimmeridgian tithonian unit at the top they are discussed in terms of chlorine budget and hydrogeological processes clay pore waters and aquifer waters show strong chlorine concentration depletion a steep cl concentration gradient from the dogger at 500m in depth 2500 mg l to the oxfordian kimmeridgian tithonian aquifer near the surface 10 mg l is associated to a v shaped profile of the 37cl values modelling cl transport shows that a hydrodynamic dispersion process explains cl concentration and 37cl profiles in oxfordian limestone this process implies a mean upward flux of chloride in the 2 6 10 8 8 2 10 8 mole m2 yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride the modelling and knowledge of underground water transfer suggest a maximum effective cl hydrodynamic vertical dispersion coefficient vertical cl transport coefficient of 7 6 10 10 m2 s chlorine transfer through the callovo oxfordian clay since deposition 160my ago can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events such as early diffusion ion filtration etc

chemical and isotopic characterization of hydrocarbon gas traces in porewater of very low permeability rocks the example of the callovo oxfordian argillites of the eastern part of the paris basin abstract a methodology has been developed to determine chemical and carbon isotopic compositions of trace amounts of hydrocarbon gas compounds methane ethane propane iso and normal butane present as dissolved compounds in the porewater of the low permeability callovo oxfordian argillites in eastern paris basin france results indicate that the studied hydrocarbons contain significant amounts of ethane butane and propane in addition to methane carbon isotopic compositions reflect primarily thermogenic origin thermal cracking of organic matter and lack of any significant biodegradation because temperature did not exceed 50 c in the studied argillites investigated hydrocarbons must have originated in hotter deeper organic bearing formations possibly stephanian coals data supports the predominance of high maturity thermogenic gas in the upper part of the callovo oxfordian and low maturity thermogenic gas mixed with minor bacterially produced methane in the lower part of the formation a mixing between three end member gases models quite well the data one thermogenic gas with a low maturity 42 methane with a 13 c of 53 a gas with higher maturity 55 methane with a 13 c of 47 and a bacterial gas 99 45 methane with a 13 c of 80 this study illustrates that migration of hydrocarbon gases can take place in rocks with very low permeability and porosity such as compacted mudrocks given enough time it further suggests that the studied fluid migration and transfer in aquitards would help characterization and understanding of fluid movements in sedimentary basins as a complement to studies focused on water aquifers and hydrocarbon reservoirs chemical and isotopic composition of dissolved hydrocarbons in porewater can be used as natural tracers of fluid circulation in sedimentary basins in addition to more conventional tracers

the structure and evolution of a numerically simulated high precipitation supercell thunderstorm the structure and evolution of a high precipitation hp supercell thunderstorm is investigated using a threedimensional nonhydrostatic cloud scale numerical model tass the model is initialized with a sounding taken from a mesoscale modeling study of the environment that produced the 28 november 1988 raleigh tornadic thunderstorm tass produces a long lived convective system that compares favorably with the observed raleigh tornadic thunderstorm the simulated storm evolves from a multicell type storm to a multiple updraft supercell storm the storm complex resembles a hybrid multicell supercell thunderstorm and is consistent with the conceptual model of cool season strong dynamic hp supercells that are characterized by shallow mesocyclones the origin of rotation in this type of storm is often in the lowest levels interactions between various cells in the simulated convective system are responsible for the transition to a supercellular structure an intense low level updraft core forms on the southwest flank of the simulated storm and moves over a region that is rich in vertical vorticity the stretching of this preexisting vertical vorticity in the storm s lowest levels is the most important vertical vorticity production mechanism during the initial stages of the main updraft s development interactions with an extensive cold pool created by the storm complex are also important in producing vertical vorticity as the main updraft grows overall the development of vorticity associated with the main updraft appears similar to nonsupercellular tornadic storms however classic supercell signatures are seen early in the simulation associated with other updrafts e g formation of vortex couplet due to tilting of ambient horizontal vorticity storm splitting etc and are deemed important in the storm s supercell stage rotation is sustained in the lowest levels of the storm despite large amounts of precipitation located near and within the main mesocyclone pulsating downdrafts periodically invigorate the storm and the gust front never occludes thus allowing the main updraft to persist for a prolonged period of time the storm s intensity is also maintained by frequent updraft mergers

possible effects of erosional changes of the topographic relief on pore pressures at depth formation fluid pressures are said to be anomalous or abnormal if they differ from hydrostatic for the depth considered explanations of the origin and maintenance of anomalies seldom include the possibility of delayed adjustment of subsurface pore pressures to erosional modifications of the topographic relief yet the present paper shows that it is entirely possible for subaerial erosion to generate pore pressure changes at great depths by cross formational energy transfer in realistic field conditions conversely pressures may survive changes in the topography and be in a transient state for hundreds to millions of years thus appearing anomalous at the time of observation according to calculations for the red earth region in alberta canada present pore pressures in the devonian immediately above the precambrian basement at a depth of approximately 1400 meters may have been induced originally by erosionally shaped topography during pliocene times 12 to 1 m y b p but be adjusting now to new boundary conditions created by the erosional exposure of the sub cretaceous unconformity a 12 adjustment may already have taken place during the last 300 thousand years leaving nearly 90 of pliocene age pressures to survive to date as slowly decaying transient pressure relicts of the geologic past in view of the possible erosional effects on pore pressures demonstrated in this paper the question of anachronous formation pressures may deserve consideration in problems related to deep basin hydrology including regional groundwater resource development migration and accumulation of hydrocarbons radioactive waste isolation dating of various geologic events and so on

geochemical evidence for efficient aquifer isolation over geological timeframes aquitards layers of rock having low permeability have been suggested as potential long term reservoirs for toxic materials such as nuclear or chemical waste but information about the isolation properties of aquitard layers is essential to evaluate whether they can indeed be used safely as reservoirs here we investigate the long term mobility of groundwaters between two aquifers surrounding an aquitard layer in the eastern recharge area of the paris basin france using helium isotopes as a geochemical tracer the deeper trias sandstone aquifer which lies above the crystalline basement accumulates radiogenic 4he and primordial 3he from large regions of the crust and mantle at rates comparable to the degassing of the whole crust1 and of mid ocean ridges2 we show that the overlying carbonate dogger aquifer which is separated from the trias aquifer by an aquitard layer consisting of a 600 m succession of shales and clays is stagnant and has been extremely well isolated from the trias over the past several million years this finding together with previous studies at the centre of the paris basin3 4 shows that diffusive mass transfer across aquitards is negligible and that cross formational flow in basins takes place preferentially in faulted areas

generation of high pore pressures in accretionary prisms inferences from the barbados subduction complex recent geological and geophysical exploration of several accretionary complexes reveals that pore pressures inside them are much higher than the hydrostatic values indirect inferences further suggest that such high pore pressures may be present inside most accretionary complexes in this study the mechanisms for generating excess pore pressures is investigated by focusing on the barbados ridge complex which is an end member of sediment rich accretionary prisms modeling is carried out using a two dimensional finite element procedure with constraints provided by the following data deep sea drilling project results on stratigraphy and lithology seismic results on sediment structure and thickness regional geology on tectonic history and laboratory measurements on mechanical properties of sediments coupling among the equations for fluid flow heat transfer and sediment deformation is made throughout the computation the results of the modeling predict that the principal decollement beneath the barbados ridge complex is a zone of high pore pressure high porosity and reversal in seismic velocity these characteristics may be responsible for the mechanical weakness of the decollement which allows continuous subduction of sediments below it and for its seismic signatures results of the modeling further suggest that tectonic overburden may be the most important mechanism for the generation of high pore pressures inside accretionary prisms the direct effect of tectonic compression is of secondary importance and the effect due to temperature increase with subduction is of little significance thrust faulting near the toe of accretionary prisms can disturb pore pressure patterns and produce localized highs rich sediment supply low permeability high subduction angle and high subduction velocity are all favorable factors in creating high pore pressures inside accretionary prisms

characterization of transport properties of argillaceous sediments application to the callovo oxfordian argillite 1 we consider the case of a cylindrical cored specimen of a saturated argillaceous sediment located between two reservoirs filled with an electrolyte one of the boundaries of the sample is submitted to a sharp pressure or salinity change the migration of the resulting pressure or saline front through the core specimen is responsible for the apparition of an electrical field which is called the streaming potential the diffusion potential for a salinity gradient respectively the temporal variation of this electrical field is recorded with ag agcl nonpolarizable electrodes and used to monitor the evolution of the pressure or saline front between the two reservoirs there is a finite interval of time before which the steady state condition holds through the core in both cases the electrical potentials exhibit a relaxation with a relaxation time constant depending on the square of the length of the cylindrical core specimen and on its hydraulic or ionic diffusivity the experiments described here provide new methodologies to determine the hydraulic and ionic diffusivities of clay rich materials these experiments confirm also the predictions of a transport model developed recently for such materials and illustrate a powerful geophysical method to obtain transport properties not only in the laboratory but also in the field using a network of nonpolarizable electrodes to remotely monitor dissipation processes occurring inside the investigated system

simulation of the parma river blockage by the corniglio landslide northern italy abstract near the village of corniglio in the northern apennines about 40 km sw of parma a big landslide was recently 1994 1996 subjected to reactivation damaging many buildings and partially obstructing the parma river in this work we have carried out a quantitative analysis of the recent evolution of the landslide with the help of a geographic information system gis in order to predict the most plausible future developments then various simulations of landslide descent were carried out and above all to evaluate the possibility of blockage formation to this purpose two computer programs that simulate the material descent through a cellular automata model and define blockage characteristics were written many different simulations were carried out 16 of which are presented here for each of them the computer output consists of a table defining the quantity of displaced material area and volume of the dam and lake and of a map showing the areas involved in the landslide movement and upstream flooding in order to assess the probability of blockage formation and dam stability we applied the simulation results to some empirical rules defined by preceding authors through statistical analysis carried out on a high number of analogous phenomena these rules suggest that it is very unlikely that blockage takes place as the result of very slow landslide velocity riverbed width and high erodibility of the material if it were to occur the size and shape of the dam seem sufficient to guarantee a considerable degree of stability making a sudden failure improbable

susceptibility and triggering scenarios at a regional scale for shallow landslides abstract the work aims at identifying susceptible areas and pluviometric triggering scenarios at a regional scale in calabria italy with reference to shallow landsliding events the proposed methodology follows a statistical approach and uses a database linked to a gis that has been created to support the various steps of spatial data management and manipulation the shallow landslide predisposing factors taken into account are derived from i the 40 m digital terrain model of the region an 15 075 km2 extension ii outcropping lithology iii soils and iv land use more precisely a map of the slopes has been drawn from the digital terrain model two kinds of covers prevalently coarse grained cg cover or fine grained fg cover were identified referring to the geotechnical characteristics of geomaterial covers and to the lithology map soilscapes were drawn from soil maps and finally the land use map was employed without any prior processing subsequently the inventory maps of some shallow landsliding events totaling more than 30 000 instabilities of the past and detected by field surveys and photo aerial restitution were employed to calibrate the relative importance of these predisposing factors the use of single factors first level analysis therefore provides three different susceptibility maps second level analysis however enables better location of areas susceptible to shallow landsliding events by crossing the single susceptibility maps on the basis of the susceptibility map obtained by the second level analysis five different classes of susceptibility to shallow landsliding events have been outlined over the regional territory 8 9 of the regional territory shows very high susceptibility 14 3 high susceptibility 15 moderate susceptibility 3 6 low susceptibility and finally about 58 very low susceptibility finally the maps of two significant shallow landsliding events of the past and their related rainfalls have been utilized to identify the relevant pluviometric triggering scenarios by using 205 daily rainfall series different triggering pluviometric scenarios have been identified with reference to cg and fg covers a value of 365 mm of the total rainfall of the event and or 170 mm d of the rainfall maximum intensity and a value of 325 mm of the total rainfall of the event and or 158 mm d of the rainfall maximum intensity are able to trigger shallow landsliding events for cg and fg covers respectively the results obtained from this study can help administrative authorities to plan future development activities and mitigation measures in shallow landslide prone areas in addition the proposed methodology can be useful in managing emergency situations at a regional scale for shallow landsliding events triggered by intense rainfalls through this approach the susceptibility and the pluviometric triggering scenario maps will be improved by means of finer calibration of the involved factors

the influence of preexisting boundaries on supercell evolution abstract a three dimensional nonhydrostatic cloud model is used to study the evolution of supercell thunderstorms with emphasis on the low level mesocyclone interacting with preexisting boundaries the impacts of low level environmental shear storm motion relative to boundary orientation and boundary strength are assessed in the low level shear experiments significant low level rotation is consistently observed earlier tends to be stronger and is longer lived in storms interacting with a boundary than in storms initiated in a homogeneous environment low level rotation is weaker in storms crossing the boundary and moving into the colder air in contrast all storms moving along or into the warm air ahead of the boundary develop significant low level rotation increasing the temperature gradient and shear across the boundary has little impact on the low level mesocyclone evolution storms interacting with a boundary characterized by only horizontal shear produce weaker mesocyclones than those creat

a nontectonic origin for the present day stress field in the paris basin france the large scale stress patterns observed in intra plate areas are often considered to result from far field boundary forces that drive plate tectonics however no present day deformation has been detected in the french paris basin yet significant deviatoric stresses are measured in limestone formations observed above soft argillite layers encountered in this region further the pore pressure measured in the argillite is larger than that measured in the surrounding permeable zones these observations suggest a presently active source of stress in this sedimentary system we propose that this stress field is not related to tectonics but only to gravity acting on the series of visco elastic orthotropic geomaterials that fill up the basin this visco elastic response is linked to pressure solution effects activated by pore pressure transients related to climatic variations these pressure transients develop in the fracture system that affects some of the geomaterials and imply a time dependant deformation field with time constants related to those of climatic variations this model outlines the influence of time dependent material properties on the present day stress and pore pressure fields that prevail at various depths it may be considered as a possible loading mechanism for the analysis of intra plate seismicity

analysis of time varying rainfall infiltration induced landslide a case study of rainstorm induced landslide is modeled following the hourly rainfall time series from the stage of infiltration caused by induced slope movement and soil saturated to excess pore pressures transient rainfall infiltration and grid based regional slope stability analysis trigrs the grid based landslide stability analysis was conducted to model the increased pore pressures and runoff in the study area under the specified rainfall conditions the generated time variances of pore pressures help determine landslide characteristics and mechanisms under rainfall conditions inputs of soil properties and permeability parameters for landslide stability analysis in the study area were prepared by trigrs adopted for transient infiltration analysis results of the analyses show that under heavy rainfall conditions the infiltrated slope is unstable and the time of debris masses movement initiated is correlated to the recorded time in the initiated landslide characteristics and effects are considered and reflected in the numerical modeling under combinations of topography land use climatic and geological conditions results reveal that there is a plane failure surface and a potential circular failure surface at the study site besides the rock topple failures in the crest a grid based slope stability analysis incorporated with the gis spatial functions is more advantageous than the traditional two dimensional analysis for specified slope profiles to determine the whole behavior of a slope

sealing efficiency of shales the sealing efficiency of shale layers is studied through the hydraulic parameters which are required for sustaining overpressure during geologically significant periods assuming a 1d sedimentary complex composed of a sealing layer overlying a permeable one we give approximate solutions for the dissipation of a given initial overpressure the time constant for relaxation involves the thickness hydraulic conductivity and specific storage of the seal and also those of the permeable layer the values of the various hydraulic parameters are discussed it is argued first that the specific storage corresponding to plastic deformation during burial compaction is larger than the one which would correspond to elastic deformation when taking into account i plausible values for specific storage of the upper shale layer and ii the storage effect of the lower permeable layer it is found that a shale layer of several tens of m with an hydraulic conductivity of the order of 10 15 ms 1 maintains overpressure for 1 myr for such hydraulic parameter values in the absence of on going pressuring forces initial overpressures would decay with a time constant corresponding to a decrease by a factor e 2 7 of 1 myr this is interpreted as supporting a dynamic origin for observed abnormal pressures

an unusual hailstorm on 24 june 2006 in boulder colorado part i mesoscale setting and radar features abstract an unusual isolated hailstorm descended on boulder colorado on the evening of 24 june 2006 starting with scattered large flattened disk shaped hailstones and ending with a deluge of slushy hail that was over 4 cm deep on the ground the storm lasted no more than 20 min and did surprisingly little damage except to vegetation part i of this two part paper examines the meteorological conditions preceding the storm and the signatures it exhibited on weather surveillance radar 1988 doppler wsr 88d displays there was no obvious upper tropospheric forcing for this storm vertical shear of the low level wind was minimal the boundary layer air feeding the storm was not very moist maximum dewpoint 8 5 c and convective available potential energy calculated from a modified air parcel was at most 1550 j kg 1 despite these handicaps the hail producing storm had low level reflectivity exceeding 70 dbz produced copious low density hail exhibited strong rotation and generated three extensive bo

determination of principal stress magnitudes using calcite twins and rock mechanics data abstract this paper proposes a new method for determining principal stress magnitudes based on the use of the deviatoric stress tensor determined from computer inversion of calcite twin data additional evaluation of the vertical stress weight of overburden or of the mean stress is enough to calculate the complete stress tensor we emphasize that the best reasoning consists of combining calcite twin analysis with rock mechanics data failure friction criteria because the determination of the six parameters of the absolute stress tensor is overconstrained