middle holocene aeolian activity on the high plains of west central kansas the uppermost surficial stratigraphic unit south of the arkansas river in the kansas high plains is a previously unidentified middle holocene or younger loess the unit fits both a loess thickness and a particle size model for loess distribution with increasing distance from source a soil immediately below this unit is radiocarbon dated 6000 to 6700 years bp the radiocarbon ages indicate that the loess unit is younger than the commonly reported ranges for bignell loess in the great plains and demonstrate a need for re examining holocene loess stratigraphy of the great plains in some locations closest to the arkansas valley source this middle holocene unit is overlain by or interfingers with dune sands the presence of these aeolian sands indicates that following a period of relative landscape stability and soil development a shift toward a middle holocene climate in which aeolian processes dominated occurred about 6000 years ago on the high plains of west central kansas

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

radiocarbon dating of soil organic matter radiocarbon ages of soil organic matter are evaluated with a model which incorporates the dynamics of the14c content of soil organic matter measured14c ages of soil organic matter or its fractions are always younger than the true ages of soils due to continuous input of organic matter into soils differences in soil c dynamics due to climate or soil depth will result in significantly different14c signatures of soil organic matter for soils of the same age as a result the deviation of the measured14c age from the true age of soil formation could differ significantly among different soils or soil horizons our model calculations also suggest that14c ages of soil organic matter will eventually reach a steady state provided that no climatic or ecological perturbations occur once a soil or a soil horizon has reached a steady state 14c dating of soil organic matter will provide no useful information regarding the age of the soil however for soils in which steady state has not been reached it is possible to estimate the age of soil formation by modeling the measured14c contents of soil organic matter radiocarbon dating of buried soils could in general overestimate the true age of the burial by as much as the steady state age of the soil or soil horizon

a high resolution record of holocene climate change in speleothem calcite from cold water cave northeast iowa high precision uranium thorium mass spectrometric chronology and 18o 13c isotopic analysis of speleothem calcite from cold water cave in northeast iowa have been used to chart mid holocene climate change significant shifts in 18o and 13c isotopic values coincide with well documented holocene vegetation changes temperature estimates based on 18o 16o ratios suggest that the climate warmed rapidly by about 3 c at 5900 years before present and then cooled by 4 c at 3600 years before present initiation of a gradual increase in 13c at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present

leakage detection of water reservoirs using a mise a la masse approach abstract localizing leaks of water and fluids from storage tanks and water reservoirs with geomembranes is an important task for a variety of environmental applications and water resources applications the minimally intrusive mise a la masse method is used to detect leaks with the current injected inside the reservoir and a return current electrode located remotely we test a new approach for the inversion of the voltage data using sandbox experiments and numerical modeling a method similar to the self potential inversion method is proposed to inverse the voltages recorded around the tank or reservoir a global objective function with a data misfit term and regularization term is minimized to invert the voltages in the inversion process a depth weighting matrix is used to strengthen the depth resolution of the current source and the minimum support method is used to avoid oversmoothed results in terms of leak detection the distributions of electrical current density on the walls of reservoir indicate the position of leaks the results show that the inversion method with source compaction accurately identifies the location of single leaks for two separated leaks there is an obvious bias for the deeper hole and the bias increases with its depth for three holes the source compaction method generally identifies the location of the three leaks when their depth ranges are similar when one of the leaks becomes deeper localization of the deeper one becomes more difficult the influence of the size of the leak on the inversion results is also investigated the inversion algorithm overestimates the depth of small leaks while it slightly underestimates the depth of large leaks for a leak having the form of a crack the inversion results using the source compaction method agree with the position of the leak and its shape

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

application of the mise a la masse method to detect the bottom leakage of water reservoirs abstract leakages of reservoirs are responsible for the loss of water resources and the spread of contaminants we develop a methodology to detect leaks located at the bottom side of a reservoir with the minimally invasive mise a la masse method which involves the potential electrodes located at the ground surface around the reservoir and the current source and sink placed in and out of the reservoir respectively this method allows localizing the secondary current distribution associated with leakage using the distribution of potential recorded on a set of electrodes during the mise a la masse experiment an initial model based on the distribution of root mean square values between the observation and the simulation data is first given to the inversion algorithm the tikhonov regularization which includes a weighting matrix and a minimum support function is used to strengthen the detection resolution of the leak 29 sandbox experiments show that the proposed method and inversion algorithm can localize a single leak for a leak with a crack shape the inversion algorithm detects the location of the leak with a small bias when the leak lasts a conductive zone may occur below the leak due to the increase of water content or ionic strength of the pore water the occurrence of such a conductive body could affect the localization of the leak because the conductivity distribution may not be well resolved the effect is analyzed using synthetic experiments the results show that the bias between the real leak and inversion results increases with the position and size of the undetected conductive zone two small scale field tests were conducted to test the performance of the mise a la masse method the two leaks are properly identified this study provides an efficient approach to detect the bottom leakage of reservoirs

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

quantifying the distribution of nanodiamonds in pre younger dryas to recent age deposits along bull creek oklahoma panhandle usa high levels of nanodiamonds nds have been used to support the transformative hypothesis that an extraterrestrial et event comet explosion triggered younger dryas changes in temperature flora and fauna assemblages and human adaptations firestone rb et al 2007 proc natl acad sci usa 104 41 16016 16021 we evaluate this hypothesis by establishing the distribution of nds within the bull creek drainage of the beaver river basin in the oklahoma panhandle the earlier report of an abundance spike of nds in the bull creek i younger dryas boundary soil is confirmed although no pure cubic diamonds were identified the lack of hexagonal nds suggests bull creek i is not near any impact site potential hexagonal nds at bull creek were found to be more consistent with graphene graphane an additional nd spike is found in deposits of late holocene through the modern age indicating nds are not unique to the younger dryas boundary nd distributions do not correlate with depositional environment pedogenesis climate perturbations periods of surface stability or cultural activity

electrical resistance tomography electrical resistance tomography ert is a method that calculates the subsurface distribution of electrical resistivity from a large number of resistance measurements made from electrodes for in situ applications ert uses electrodes on the ground surface or in boreholes it is a relatively new imaging tool in geophysics the basic concept was first described by lytle and dines as a marriage of traditional electrical probing introduced by the schlumberger brothers and the new data inversion methods of tomography development of both the theory and practice of ert was confined mostly to the late 1980s and the 1990s tomographic inversion added important new capabilities as it was more general accurate and rigorous at spatial imaging of geophysical electrical resistance data than earlier pseudosection or curve fitting methods

self potential signals associated with localized leaks in embankment dams and dikes abstract the self potential method can be used to detect and monitor anomalous seepages in dams and embankments in such a case an electrical field of electrokinetic nature i e associated with pore water flow can be measured using a set of non polarizable electrodes typically located at the ground surface or in some wells this field can be in turn related to the pattern of groundwater flow we built an experimental dam to investigate to which extent the self potential method can help characterizing seepages in dams we first use the finite element method to simulate the ground water flow in a heterogeneous porous and permeable material by solving the groundwater flow equation the resulting groundwater flow solution is then used to compute the electrical potential distribution by solving the corresponding elliptic partial differential equation in a preliminary experiment we could not measure any self potential anomaly associated with the infiltration of water in the dam our numerical simulations showed that the magnitudes of the self potential anomalies were controlled by 1 the nature of the flow regime viscous laminar versus inertial laminar flow regimes and 2 the presence of insulating polyvinyl chloride pvc tubes located at the end of the preferential flow channels in the structure of the dam thanks to these numerical simulations we added sand at the entrance of the infiltration area in order to reduce the effects of the pvc tubes and to restrain the flow regime to the viscous laminar flow regime new experiments allowed for detecting a self potential anomaly with an amplitude of around 9 mv consistent with that obtained through numerical modelling with a finite element simulator this comparison was used to test the accuracy of the modelling approach and define the strengths and weaknesses of the self potential method to determine preferential seepages in earth dam structures

paleo environmental reconstruction and bio stratigraphy oklahoma panhandle usa worldwide the period between 12 000 and 9000 radiocarbon years before present rcybp witnessed the shift from glacial to post glacial times and marks the transition from the pleistocene to the holocene on the southern plains of north america this period is marked by rapidly changing climatic conditions shifting flora and faunal associations and cultural adaptations a recently discovered locality along bull creek oklahoma panhandle provides the opportunity to study the environmental context of changing megafauna presence during this transition the paleo environment is reconstructed from sediment particle size distribution stable carbon isotope pollen and phytolith analyses from the bull creek site and compared with the megafaunal biostratigraphy in this area

identification of leakage and potential areas for internal erosion combining ert and ip techniques at the negratin dam left abutment granada southern spain abstract at the negratin dam southern spain two main springs derived from the water reservoir were detected on the west side of the mountain ridge matching the location of the left abutment of the dam the seepages appear when the level of the stored water exceeds 622 m above sea level m a s l where some paleochannels are embedded in the silts the water level was at 631 m a s l on the day of the measurements 13 12 23 close to the historical maximum 633 78 m a s l although the water crossing the leaks does not drag particles nowadays this sector may potentially cause internal erosion or piping phenomena implying a loss of water resources and slope instability problems the infiltration areas were evaluated by electrical resistivity and induced polarization methods measured along one profile on the mountain ridge between the water reservoir and the springs we determine that the infiltrations zones are characterized by low resistivity and high chargeability distributed in small areas we demonstrate that these methods are a reliable tool to detect and characterize infiltration zones and they are the first step to planning mitigation actions to avoid the piping phenomena

model shows that rivers transmit high frequency climate cycles to the sedimentary record rivers are a major component of sediment routing systems that control the transfer of terrigenous sediments from source to sink although it is widely accepted that rivers are perturbed by millennial scale climatic variability the extent to which these signals are buffered or transferred down river systems to be recorded in sediments at or beyond the river mouth remains debated here we employ a physically based numerical model to address this outstanding issue our model shows that river transport strongly amplifies high frequency sediment flux variations arising from changing water discharge due to positive feedback between discharge and the channel gradient this behavior is distinctly different from short period sediment flux signals with constant water discharge where the output sediment flux is strongly dampened within the river due to negative feedback between the channel gradient and sediment concentration we conclude that marine sedimentary basins may record sediment flux cycles resulting from discharge and ultimately climate variability whereas they may be relatively insensitive to pure sediment flux perturbations such as for example those induced by tectonics

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

electric potential source localization reveals a borehole leak during hydraulic fracturing abstracta laboratory experiment was performed to see if passively recorded electric signals can be inverted to retrieve the position of fluid leakages along a well during an attempt to hydraulically fracture a porous block in the laboratory the cubic block was instrumented with 32 nonpolarizing sintered ag agcl electrodes during the test several events were detected corresponding to fluid leakoff along the seal of the well each event showed a quick burst in the electric field followed by an exponential type relaxation of the potential distribution over time the occurrence of these electric events was always correlated with a burst in the acoustic emissions and a change in the fluid pressure these self potential data were inverted in two steps 1 using a deterministic least square algorithm with focusing to retrieve the position of the source current density in the block for a given snapshot in the electric potential distribution and 2 using a genetic algorithm to refine the position of the sou

induced polarization tomography applied to the detection and the monitoring of leaks in embankments abstract during an induced polarization survey both electrical conductivity and chargeability can be imaged recent petrophysical models have been developed to provide a consistent picture of these two parameters in terms of water and clay contents of soils we test the ability of this method at a test site in which a controlled artificial leakage can be generated in an embankment surrounding an experimental basin 3d tomography of the conductivity and normalized chargeability are performed during such a controlled leakage conductivity and induced polarization measurements were also performed on a core sample from the site the sample was also characterized in terms of porosity and cation exchange capacity combining the 3d survey and these laboratory measurements a 3d tomogram of the relative variation in water content before leakage and during leakage was estimated it clearly exhibits the ground water flow path through the embankment from the outlet of the tube used to generate the leak to the bottom of the embankment in addition a self potential survey was performed over the zone of leakage this survey evidences also the projection of the ground water flow path over the ground surface both methods are found to provide a consistent picture a 2 5d time lapse tomography of the electrical conductivity and normalized chargeability was also performed and evidences the position of the preferential flow paths below the profile these results confirm the ability and efficiency of induced polarization to provide reliable information pertaining to the detection of leakages in dams and embankments

time lapse mise a la masse measurements and modelling for tracer test monitoring in a shallow aquifer abstract the main goal of this study is to evaluate the reliability of the mise a la masse malm technique associated with saline tracer tests for the characterization of groundwater flow direction and velocity the experimental site is located in the upper part of the alento river alluvial plain campania region southern italy in this paper we present the hydrogeological setting the experimental setup and the relevant field results subsequently we compare those data against the simulated results obtained with a 3d resistivity model of the test area coupled with a model describing the advection dispersion equation for continuous tracer injection in particular we calculate a series of 3d forward solutions starting from a reference model all derived from electrical tomography results but taking into consideration different values of mean flow velocity and directions each electrical resistivity 3d model is used to produce synthetic voltage maps for malm surveys finally the synthetic malm voltage maps are compared with the ones measured in the field in order to assess the information content of the malm dataset with respect to the groundwater field characteristics the results demonstrate that the information content of the malm data is sufficient to define important characteristics of the aquifer geometry and properties this work shows how a combination of three dimensional time lapse modeling of flow tracer transport and electrical current can substantially contribute towards a quantitative interpretation of malm measurements during a saline tracer test this approach can thus revive the use of malm as a practical low cost field technique for tracer test monitoring and aquifer hydrodynamic characterization

hydrologic characteristics of a large rockfill dam implications for water leakage abstract the unmun dam a rockfill dam with a clay core filter zone and sandy gravel shell is located in the nakdong river basin near cheongdo gun in korea in the dam area the cretaceous gyeongsang supergroup andesite lies over intrusive granite these form the intrusive contact near the main dam and cofferdam areas the stratigraphic units in upward sequence consist of cretaceous granite and andesite weathered soft rock and a soil layer of silty clay with gravel the reservoir was first filled in august 1994 and was full by april 1998 right after complete filling three sinkholes were found in the dam crest near stations 2 12 and 10 when the reservoir level was at around 150 m the amount of leakage increased with rise of the reservoir level mainly caused by rainfall events as a countermeasure for the abnormal leakage and dam rehabilitation comprehensive surveys were performed on the dam including observational drillings grouting geophysical surveys and tracer tests by korea water resources corporation kowaco there were also further investigations for hydrologic characterization of the dam to identify water leakages the groundwater levels at the 26 observation wells installed on the crest and dam toe were measured to evaluate the relationship between the reservoir level and groundwater level and the influences on the dam leakage groundwater level at the left side of the embankment was high compared with a normal phreatic line it was only 4 m lower than the reservoir level while 6 65 m lower than that at its right side fluctuation of the groundwater levels in the crest wells coincided well with the reservoir level without a significant lag time which reflected a good hydraulic connection between the reservoir and the dam interior hydraulic conductivity estimated from 149 hydraulic tests at 9 monitoring wells constructed in the dam core showed a wide range between 1 42 10 4 and 4 35 10 8 cm s with a geometric mean of 3 13 10 6 cm s furthermore water quality at the monitoring wells were much different from that of the reservoir high levels of turbidity and electrical conductivity were observed at the monitoring wells in the left side of the bank all these hydrologic characteristics reflected possible occurrence of the leakage on the dam especially in the left embankment this paper presents a summary of several investigation studies on the hydrologic characteristics of the rockfill dam which implied abnormal water leakage

stable carbon isotopes c3 c4 vegetation and 12 800years of climate change in central new mexico usa abstract a thick sequence of fine textured alluvium in central new mexico has provided an opportunity to reconstruct vegetation type and climate at the western edge of the great plains grassland the analysis of thirty eight ams radiocarbon ages 13 c values and modern weather data has produced a 12 800 cal yr record of changing c 3 c 4 vegetation temperature and precipitation the record begins with the younger dryas that was characterized by c 3 plants and was about 2 4 c cooler with over 100 mm rainfall than today after 11 000 cal yrs bp the climate became less cool and less wet reaching present day conditions by 9000 yrs the middle holocene was c 4 warm and dry although the 13 c record is incomplete for this interval from 3300 to 1400 cal yrs bp the climate was cool and wet with c 3 plants averaging 0 5 c cooler and 22 mm greater rainfall than today matching other records in the region for a wetter climate after 1400 cal yrs bp the local climate became warm and dry shifting to c 4 vegetation the severe second century drought first observed in tree rings in southern colorado is supported by the 13 c data and occurred during the interval a d 40 to a d 180 hiatuses in the local alluvial and 13 c record extend from 9000 to 6000 cal yrs bp and from 1000 cal yrs bp to present

development of the mixed conifer forest in northern new mexico and its relationship to holocene environmental change chihuahuenos bog 2925 m in the jemez mountains of northern new mexico contains one of the few records of late glacial and postglacial development of the mixed conifer forest in southwestern north america the chihuahuenos bog record extends to over 15 000 cal yr bp an artemisia steppe then an open picea woodland grew around a small pond until ca 11 700 cal yr bp when pinus ponderosa became established c n ratios 13c and 15n values indicate both terrestrial and aquatic organic matter was incorporated into the sediment higher percentages of aquatic algae and elevated c n ratios indicate higher lake levels at the opening of the holocene but a wetland developed subsequently as climate warmed from ca 8500 to 6400 cal yr bp the pond desiccated in what must have been the driest period of the holocene there c n ratios declined to their lowest holocene levels indicating intense decomposition in the sediment wetter conditions returned after 6400 cal yr bp with conversion of the site to a sedge bog as groundwater levels rose higher charcoal influx rates after 6400 cal yr bp probably result from greater biomass production rates only minor shifts in the overstory species occurred during the holocene suggesting that mixed conifer forest dominated throughout the record

geomorphic and sedimentary responses of the bull creek valley southern high plains usa to pleistocene and holocene environmental change abstract fluvial geomorphology and stratigraphy often reflect past environmental and climate conditions this study examines the response of bull creek a small ephemeral creek in the oklahoma panhandle to environmental conditions through the late pleistocene and holocene fluvial terraces were mapped and their stratigraphy and sedimentology documented throughout the course of the main valley based on their elevations terraces were broadly grouped into a late pleistocene fill terrace t3 and two holocene fill cut terrace sets t2 and t1 terrace systems are marked by similar stratigraphies recording the general environmental conditions of the time sedimentary sequences preserved in terrace fills record the transition from a perennial fluvial system during the late glacial period and the younger dryas to a semiarid environment dominated by loess accumulation and punctuated by flood events during the middle to late holocene the highest rates of aeolian accumulation within the valley occurred during the early to middle holocene our data provide significant new information regarding the late pleistocene and holocene environmental history for this region located between the well studied southern and central high plains of north america

catastrophic landslide induced by typhoon morakot shiaolin taiwan abstract typhoon morakot induced the catastrophic and deadly shiaolin landslide in southern taiwan on 9 august 2009 resulting in more than 400 casualties we undertook a geological and geomorphological investigation with the aim of reconstructing the events leading up to this landslide and to clarify factors that contributed to its development cumulative rainfall reached up to 1676 5 mm in about three days under the influence of the typhoon and the shiaolin landslide with a volume of 25 106 m3 occurred one day after the peak in rainfall intensity the landslide occurred on a dip slope overlying late miocene to early pliocene sedimentary rocks consisting of silty shale massive mudstone and sandstone it started as a rockslide in the upper third of the landslide area and transformed into a rock avalanche that crossed a series of terraces and displaced or buried the village below it buried the riverbed of the chishan river and ran up the opposite slope creating a landslide dam 60 m high which was breached about 1 h and 24 min later flooding the village the velocity of the landslide is estimated to have been 20 4 to 33 7 m s 1 and its apparent friction angle was 14 which indicates its high mobility the detachments in the source area consist of combinations of bedding planes and joints or faults the landslide was preceded by gravitational deformation which appeared as hummocky landforms before the landslide and as buckle folds exposed after the event the landslide deposits consist of fragments of mudstone shale and sandstone as well as clayey material at its base this clayey material consisting of illite chlorite quartz feldspar and calcite is assumed to have strongly influenced the long rapid runout

holocene climate variability in texas usa an integration of existing paleoclimate data and modeling with a new high resolution speleothem record abstract delineating the climate processes governing precipitation variability in drought prone texas is critical for predicting and mitigating climate change effects and requires the reconstruction of past climate beyond the instrumental record we synthesize existing paleoclimate proxy data and climate simulations to provide an overview of climate variability in texas during the holocene conditions became progressively warmer and drier transitioning from the early to mid holocene culminating between 7 and 3 ka thousand years ago and were more variable during the late holocene the timing and relative magnitude of holocene climate variability however is poorly constrained owing to considerable variability among the different records to help address this we present a new speleothem nbj reconstruction from a central texas cave that comprises the highest resolution proxy record to date spanning the mid to late holocene nbj trace element concentrations indicate variable moisture conditions with no clear temporal trend there is a decoupling between nbj growth rate trace element concentrations and 18o values which indicate that i the often direct relation between speleothem growth rate and moisture availability is likely complicated by changes in the overlying ecosystem that affect subsurface co2 production and ii speleothem 18o variations likely reflect changes in moisture source i e proportion of pacific vs gulf of mexico derived moisture that appear not to be linked to moisture amount

detection of seepage paths in earth dams using self potential and electrical resistivity methods abstract earth and rockfill dams are designed to operate under steady state seepage anomalous seepage may be a threat to the integrity of the structure in spite of advances made in the fields of geotechnical engineering it is not possible to have 100 leak proof structure any excessive and unplanned seepage may lead to the failure of the dam especially in unconsolidated or fractured terrains geophysical methods play an important role in mapping seepage paths and monitoring the changes of the seepage with time enabling to plan technically and economically worthwhile remedial measures in the present paper utilisation of electrical methods for delineation of seepage zones at two of the four saddle dams of the som kamla amba project rajasthan state india which is founded on heterogeneous rock mass is discussed electrical resistivity method was used to delineate zones favourable for seepage whereas self potential sp method was used to delineate the seepage paths sp measurements have shown negative anomaly of the order of 10 20 mv in amplitude indicating low seepage coinciding with the seepage measurements made by the project authorities

three dimensional inversion of self potential data used to constrain the pattern of groundwater flow in geothermal fields 1 we propose an algorithm to invert self potential signals measured at the ground surface of the earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems the self potential signals result from the divergence of the streaming current density groundwater flow can be either driven by topography of the water table free convection or deformation of the medium the algorithm includes the electrical resistivity distribution of the medium obtained independently by dc resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements inversion of the distribution of the source current density from ground surface and borehole self potential measurements is achieved by solving the inverse problem using tikhonov regularization solutions that are compatible with the physics of the primary flow problem by introducing assumptions regarding the smoothness or the compactness of the source and the three dimensional distribution of the electrical resistivity of the system the inverse problem can be solved in obtaining the three dimensional distribution of the current source density in the ground however an annihilator can be added to the inverted source geometry without affecting the measured self potential field annihilators can be obtained from boundary conditions synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm an application is presented to the geothermal field of cerro prieto baja california mexico using literature data inversion of the self potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part the temperature anomaly associated with the existence of this plume is independently observed by interpolating borehole temperature measurements we found a good agreement between the distribution of the temperature and the inverted source current density the proposed method appears therefore as a noninvasive method for remote detection and three dimensional mapping of subsurface groundwater flow

grassland vegetation in the southern great plains during the last glacial maximum abstract new pollen records from white lake in the southern high plains and from friesenhahn cave on the southeastern edwards plateau of texas indicate that the glacial age vegetation of the southern great plains was a grassland the high plains was a treeless artemisia grassland and the edwards plateau at the south edge of the great plains was a grassland with pinyon pines and deciduous trees in canyons and riparian habitats the glacial age grasslands differ from modern shortgrass and tallgrass prairies and may have no modern analog the dominance of prairie vegetation during the last glacial maximum is compatible with late pleistocene mammalian faunas and late glacial grassland pollen records from the region earlier interpretations of a pine spruce forest on the high plains were based on pollen assemblages that are here shown to have been altered by postdepositional deterioration resulting in differential preservation of conifer pollen grains accordingly the tahoka pluvial and other climatic episodes defined by high plains pollen records are abandoned

headwater channel dynamics in semiarid rangelands colorado high plains usa incised ephemeral channels provide a window into the fluvial processes that help sculpt rangeland landscapes this paper presents observations of ephemeral channels and valley networks in the high plains of colorado usa with an eye toward painting a picture of the ingredients that must be included in mathematical models of landscape evolution in such environments channel incision in the study area is driven by summer thunderstorms which can with reasonable frequency 3 5 yr generate boundary shear stresses high enough to penetrate the highly resistant vegetation armor but only within erosional hot spots where hydraulic forces are amplified by channel constriction and locally steep gradients focusing of erosion at these hot spots which correspond to knickpoints and channel heads is amplified by the small areal footprint and short erosional reach of most convective storms upstream migration of knickpoints creates a pattern of short active channel reaches separated by unchanneled or weakly channeled fully vegetated stable reaches based on our observations we interpret the necessary and sufficient conditions leading to the observed channel forms and dynamics as 1 a resistant vegetation layer overlying an erodible substrate which sets up a conditional instability through which erosional perturbations can grow by positive feedback 2 high flow variability 3 moderate to high substrate cohesion and 4 a high volume fraction of fine grained erodible material concave upward valley long profiles are interpreted as a trade off between downstream increasing flood frequency and downstream decreasing flood effectiveness the observed process dynamics imply that long term rates of valley incision should be especially sensitive to climatic oscillations between episodes of drought and warm season convective rainfall

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

human responses to middle holocene altithermal climates on the north american great plains abstract the climate of the great plains during the middle holocene varied considerably but overall it was marked by a north south gradient of increasingly warmer and drier conditions with a reduction in effective moisture surface water and resource abundance and an increase in resource patchiness sediment weathering erosion and aeolian activity pronounced drought conditions were most evident on the southern high plains understanding the human responses to middle holocene climates is complicated by a lack of archaeological data which is partly a result of geomorphic processes that removed or deeply buried sites of this age and by the varying adaptive responses of hunter gatherers during this period on the southern high plains where drought was most severe surface and groundwater sources dried and bison populations were diminished prompting substantial adaptive changes including local abandonment well digging to tap underground water and a widening of the diet breadth to incorporate higher cost lower return seed and plant resources sites of this age on the central and northern plains also show a possible increase in diet breadth with the incorporation of plant foods in the diet and perhaps changes in settlement mobility including possible shift into higher elevation areas or mapping on to extant rivers and springs but linking those changes to middle holocene drought is less straightforward