accelerator mass spectrometry radiocarbon dating of rock varnish accelerator mass spectrometry ams 14c dating off rock varnish provides minimum limiting ages for landforms and archaeological artifacts in arid and semiarid lands that are undatable by conventional radiocarbon methods experiments on sample collection the effect of different individuals preparing samples the influence of different chemical extraction procedures the incorporation of carbonate detritus possible contamination from rock underlying varnish the role of bio geochemical erosion of varnish and other influences reveal procedures that yield reproducible results conventional radiocarbon dates from charcoal beneath lava flows of hualalai volcano hawaii and from arid sites in western north america provide controls to test varnish radiocarbon dating ams radio carbon ages on the very bottom layer of varnishes are typically 10 younger than the 14c ages of these controls applications are illustrated here for fluvial aeolian peri glacial hillslope lacustrine and glacial geo morphology as well as rock art research in archaeology

infra red stimulated luminescence dating of sands from the cronese basins mojave desert abstract potassium rich feldspars separated from aeolian sands from the east and west cronese basin have been dated by infra red stimulated luminescence sands from shoreline reworked aeolian dune ridges in the west cronese basin suggest that late holocene playa lakes have existed in the basin within the last 2000 years four dates from these ridges suggest that a phase of aeolian deposition and stabilisation occurred 150 250 years ago a date of 250 75 years on a yardang formed from horizontally bedded sand however implies that at least a metre of erosion in the west cronese basin has occurred since that time in response to a dominant southwesterly wind late pleistocene dates ranging from 18 850 to 23 350 years were obtained from an aeolian unit in the east cronese basin giving limiting ages on wavecut shorelines formed in the deposit this aeolian sand appears to have been deposited and stabilised at a similar time to part of the nearby cat dune sand ramp

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

in situ velocities in pelagic carbonates new insights from ocean drilling program leg 130 ontong java plateau ocean drilling program leg 130 returned an extensive suite of in situ borehole logging and closely spaced shipboard physical properties measurements from four sites drilled in carbonate rich pelagic oozes and chalks on the ontong java plateau using these data we evaluated factors responsible for observed differences between laboratory data and in situ values laboratory and log differences for bulk density porosity are small and nearly constant and can be accounted for by hydraulic rebound of pore fluid following sediment recovery evidence for mechanical rebound of sediments was not observed velocity porosity relationships cannot be used to indirectly correct laboratory velocities to in situ because fundamental assumptions required for rebound corrections are not satisfied velocity porosity systematics are also complicated by foraminiferal intraparticle porosity variations we derived empirical laboratory velocity corrections using log and laboratory velocity differences expressed as functions of depth and effective pressure we tested the velocity corrections using data for carbonates recovered from ocean drilling program sites 704 722 and 762 comparisons with logs show that corrected velocities accurately estimate in situ values for oozes and chalks caco3 60 for applications to unlogged deep sea drilling project leg 85 sites igneous basement travel times calculated using corrected velocities agree with acoustic basement travel times from seismic records implying that corrected velocities are realistic in situ estimates at site 574 we used our corrected velocities to reevaluate previous lithostratigraphic and seismostratigraphic correlations based on mechanical rebound corrected velocities the new velocities correlate reflectors to progressively greater core depths although changes are minor above 200 m below seafloor the lowest assigned reflector is shifted 36 m deeper to more closely coincide with a diagenetic boundary and acoustic basement correlates with igneous basement instead of with postulated high impedance reflectors within the sediments

evaluation of simple geochemical indicators of aeolian sand provenance late quaternary dune fields of north america revisited abstract dune fields of quaternary age occupy large areas of the world s arid and semiarid regions despite this there has been surprisingly little work done on understanding dune sediment provenance in part because many techniques are time consuming prone to operator error experimental highly specialized expensive or require sophisticated instrumentation provenance of dune sand using k rb and k ba values in k feldspar in aeolian sands of the arid and semiarid regions of north america is tested here results indicate that k rb and k ba can distinguish different river sands that are sediment sources for dunes and dune fields themselves have distinctive k rb and k ba compositions over the basin and range and great plains regions of north america the hypothesized sediment sources of dune fields are reviewed and assessed using k rb and k ba values in dune sands and in hypothesized source sediments in some cases the origins of dunes assessed in this manner are consistent with previous studies and in others dune fields are found to have a more complex origin than previously thought use of k rb and k ba for provenance studies is a robust method that is inexpensive rapid and highly reproducible it exploits one of the most common minerals found in dune sand k feldspar the method avoids the problem of using simple concentrations of key elements that may be subject to interpretative bias due to changes in mineralogical maturity of quaternary dune fields that occur over time

observations on attenuation and shear wave velocity in fine grained marine sediments compressional p wave attenuation shear s wave attenuation and shear s wave velocity measurements compiled for fine grained unconsolidated sediments show trends that do not support empirical relationships hamilton j acoust soc am 68 1313 1340 1980 in acoustics and ocean bottom f a s e specialize conf madrid 1987 commonly used for geoacoustic modeling the exception is compressional wave attenuation data from 10 hz to 500 khz that essentially follow a frequency dependence of f1 2 standard deviations p wave attenuation with depth is difficult if not impossible to predict given the variability in the data examination of several attenuation depth profiles indicates that those of mitchell and focke j acoust soc am 67 1582 1589 1980 may be the best choice for predicting p wave attenuation with depth at the present time the assumption that s wave and p wave attenuations are proportional hamilton j acoust soc am 60 334 338 1976c in acoustics and ocean bottom

field variability of landslide model parameters a data set of parameters slope soil depth and soil shear strength relevant to spatially distributed modelling of shallow landslides triggered by rain and snowmelt events was determined from field measurements in 250 grid elements of dimensions 25 m downslope 10 m across slope in an area of 250 m 250 m on a hillslope in scotland these data provide an unusually detailed basis for the evaluation of spatial variability and uncertainty in model parameterisation the variations in slope and soil strength are represented adequately by normal distributions a weibull distribution is suggested for the soil depth data the factor of safety calculated at each point in the grid was shown partially to identify observed landslides with a number of false predictions of occurrence trend analysis and semivariogram analysis of the data set suggest that the use of kriging could improve upon this approach to landslide prediction by providing areal estimates of parameters at the grid element scale with associated error bounds

equatorial pacific seismic reflectors as indicators of global oceanographic events the origin of a series of regionally correlatable seismic horizons in the neogene sediments of the central equatorial pacific is examined through seismic modeling and the detailed analyses of stratigraphic and physical property relationships in deep sea drilling project cores these regionally traceable reflectors are synchronous the younger reflectors are the direct result of carbonate dissolution events the older ones of stratigraphically selective diagenetic processes the changes in ocean chemistry associated with these events appear to be linked to global reorganizations of surface and bottom water circulation patterns the most dramatic of which are associated with reorganizations of north atlantic bottom waters these deepwater seismic horizons appear to correlate with the major events on the relative sea level curve of vail et al for the neogene

holocene dune formation at ash meadows national wildlife area nevada usa abstract small isolated dune fields in the northern mojave desert are important centers of biodiversity and archaeological occupation sites currently dunes at ash meadows nevada are stabilized by vegetation and are experiencing erosion of their upwind margins indicating a negative sediment budget new osl ages from dunes at ash meadows indicate continuous eolian accumulation from 1 5 to 0 8 ka with further accumulation around 0 2 ka prior studies e g mehringer and warren 1976 indicate periods of dune accumulation prior to 3 3 ka 1 9 1 ka and after 0 9 ka these periods of eolian accumulation are largely synchronous with those identified elsewhere in the mojave desert the composition of the ash meadows dunes indicates their derivation from regional fluvial sources most likely during periods when axial washes were active as a result of enhanced winter precipitation

luminescence dating of sand ramps in the eastern mojave desert abstract until recently the timing of the movement of sand and accumulation of sand by aeolian processes in the eastern mojave desert has remained the subject of speculation the results of a luminescence dating program involving 78 samples of material from nine sand ramp complexes have enabled recognition of regional and local patterns of sand accumulation in the eastern mojave the study area extends from lake manix in the west to the colorado river in the east the periods of accumulation have been identified on the basis of quartz tl dating and potassium feldspar tl and irsl dating at a regional scale two major depositional phases can be identified 1 late pleistocene 20 30 ka with sequences at hank s mountain balch dale lake and the big marias and 2 late pleistocene early holocene 15 7 ka with sequences at cat dune dale lake iron mountain big marias above palaeosol and at the western end of the study area at soldier mountain 20 7 ka late holocene sequences appear to be much more localized and are confined to the west cronese old dad mountain and balch sand ramps the earliest phases of sand accumulation on the ramps studied immediately predate the formation of pluvial lake mojave ca 24 5 ka the later main phases of accumulation coincide with the existence of lake mojave and the end of accumulation on the majority of the sand ramps immediately post dates the final end of intermittent lake mojave iii 9 7 ka the continuity of sand supply to potential deflation areas is seen as a critical condition for accumulation of material on the sand ramps during the late quaternary in the eastern mojave

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

gis techniques and statistical models in evaluating landslide hazard geographical information systems gis and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard from a small drainage basin located in central italy relevant geological and geomorphological factors were collected and processed by applying gis technology in particular modules were used which both generate high fidelity digital terrain models and automatically partition the terrain into main slope units the resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope unit although not lacking drawbacks the method proved to be a feasible and cost effective approach to landslide susceptibility assessment and mapping

geomorphic and hydrologic implications of the rapid incision of afton canyon mojave desert california afton canyon is a 150 m deep canyon that formed as a result of overflow and drainage of lake manix an 215 km2 late wisconsin pluvial lake in the central mojave desert because the canyon age is within the range of conventional radiocarbon dating it is possible to provide a time based chronology of events and resultant landscape changes due to a 120 m base level drop analysis of erosion volumes upstream of afton canyon and a review of public and private well logs downstream of the canyon mouth indicate that late wisconsin surfaces are deeply buried downstream of afton canyon burial depths are 55 m at the mouth of afton canyon 27 m in the cronese basin and 18 m at crucero the well logs also indicate that soda lake was far more areally extensive prior to late wisconsin time stratigraphic and geomorphic evidence suggests that afton canyon was cut rapidly sometime after 14 230 1325 yr b p the rapid draining of lake manix and subsequent basin dissection have important implications for late quaternary lake fluctuations in death valley base level changes and resultant alluvial fan adjustments in the cronese basin the sand source for the kelso dunes and the absence of old artifacts in the cronese basin and the mojave river wash region

periglacial fluvial systems in northwest europe during marine isotope stages 4 and 3 comparison of fluvial successions in river valleys dating from marine isotope mi stages 4 and 3 in a west east transect from britain to poland shows the spatial and temporal variation in palaeohydrological characteristics of northwest european river valleys during these stages mi stage 4 has been a period of deep fluvial incision following this erosion most valleys were filled during mi stage 3 with successions of gravelly river deposits britain or sand silt peat successions northwest european lowlands the sedimentology of the deposits suggests strong discharge variations caused by a nival discharge regime with pronounced spring snowmelt discharges the mi stage 3 climate oscillations generally cannot be traced in the fluvial record an incision phase of hengelo interstadial age has been found in the netherlands but similar incision phases related to other warming events have not been proved convincingly the restricted reaction of the river systems is caused by the absence of geomorphologically effective vegetation changes and relatively minor variations in precipitation during mi stage 3 over longer time scales silt and peat beds gradually decrease in the younger post hengelo upton warren part of mi stage 3 corresponding with evidence of aeolian activity and permafrost this is related to the longer duration of the stadials in this part of mi stage 3

a landslide susceptibility model using the analytical hierarchy process method and multivariate statistics in perialpine slovenia abstract landslides cause damage to property and unfortunately pose a threat even to human lives good landslide susceptibility hazard and risk models could help mitigate or even avoid the unwanted consequences resulted from such hillslope mass movements for the purpose of landslide susceptibility assessment the study area in the central slovenia was divided to 78 365 slope units for which 24 statistical variables were calculated for the land use and vegetation data multi spectral high resolution images were merged using principal component analysis method and classified with an unsupervised classification using multivariate statistical analysis factor analysis the interactions between factors and landslide distribution were tested and the importance of individual factors for landslide occurrence was defined the results show that the slope the lithology the terrain roughness and the cover type play important roles in landslide susceptibility the importance of other spatial factors varies depending on the landslide type based on the statistical results several landslide susceptibility models were developed using the analytical hierarchy process method these models gave very different results with a prediction error ranging from 4 3 to 73 as a final result of the research the weights of important spatial factors from the best models were derived with the ahp method using probability measures potentially hazardous areas were located in relation to population and road distribution and hazard classes were assessed

empirical reflection travel time versus depth and velocity versus depth functions for the deep sea sediment column numerous correlations of one way reflection travel times and depths to reflecting horizons have been proposed in the initial reports of the deep sea drilling project dsdp having carefully reviewed proposed correlations we selected 233 correlated depths ranging from 27 m to 1 4 km and one way travel times ranging from 0 02 to 0 7 s from 154 dsdp sites worldwide assuming that the velocity depth function for deep sea sediments can be approximated by an exponential form we have used these data to establish statistically well constrained global models relating depth to travel time and velocity to depth there is remarkably little scatter in the data based on nonlinear least squares fits the best depth time function is z km 3 03 1n 1 0 52t s the rms error in depth is 26 m the corresponding average velocity depth function is v km s 1 59exp 0 33z we estimate that the real site to site variability of velocities at depth is less than 0 20 km s any dependence of velocity on composition is below the resolution of the data and available evidence suggests that age has no significant effect these results imply that to a depth of 1 4 km the physical state of sediments depends on in situ overburden pressure and temperature which are related to depth of burial and that chemical and mechanical equilibrium is achieved in a period of time that is geologically short our results are consistent with laboratory measurements of p wave velocities in deep sea sediments but velocity depth functions for terrigenous and calcareous sections derived from sonobuoy wide angle reflection surveys are incompatible with the time and depth data and overestimate velocities by as much as 10 and 30 respectively these systematic errors may result from the fact that the marked anisotropy of deep sea sediments is neglected in the interpretation of reflection data

luminescence dating of mojave desert sands abstract infra red stimulated luminescence has been used to date periods of sand deposition in the mojave desert california dates from the cronese basins kelso dunes and silver lake are compared with published irsl ages to provide evidence for discrete pulses of sand accretion during the late pleistocene and holocene linked to both arid and pluvial climates a critical factor in aeolian deposition throughout this area is shown to be the availability of sand from existing source areas

short duration holocene lakes in the mojave river drainage basin southern california stratigraphic sedimentologic and pedologic studies of beach ridge and lacustrine deposits indicate that up to five times during the holocene shallow lakes covered silver lake playa in southeastern california for periods of years to decades the two youngest lacustrine events at about 390 90 yr b p and 3620 70 yr b p coincide with the early and late neoglacial episodes of north america increasing evidence in recent years from other nonglaciated areas leads us to conclude that the effects of these climatic episodes were much more widespread than previously thought the climate during these episodes was characterized by an increased frequency of winter storms in the southwestern united states causing wetter conditions that affected diverse hyperarid environments in the mojave desert and adjacent regions we propose that this wide areal coverage was caused by large scale winter atmospheric circulation patterns which are probably related to changes in sea surface temperatures and oceanic circulation in the eastern north pacific ocean

in situ acoustic properties of pelagic carbonate sediments on the ontong java plateau the ontong java plateau with its thick capping sequence of cretaceous and cenozoic pure pelagic carbonate sediments forms an ideal setting for the study of the acoustic properties of this lithology on an oceanic rise borehole logs recorded on deep sea drilling project leg 89 at site 586 provided detailed data on in situ acoustic properties of pleistocene to early miocene sediments to a depth of 623 m below seafloor comparison of these logging results and the sonobuoy based results of johnson et al 1978 with previous laboratory measurements from the ontong java plateau shows that velocity depth functions determined from the logging and sonobuoy methods are concordant but diverge significantly from functions derived from laboratory measurements log densities and compressional velocities exceed those measured by laboratory techniques the density discrepancy is strongly influenced by laboratory method the differences between log and laboratory compressional velocities are greater than and extend to greater depths than those between densities these differences can be attributed to reductions in the frame bulk modulus and dynamic rigidity caused by the removal of overburden pressure in the absence of significant porosity rebound agreement of site 586 log velocities with velocities derived from the earlier sonobuoy measurements across the plateau argues for the interpretation that both methods measure in situ values the disagreement between the site 586 log results and the sonobuoy results with both the empirical velocity depth function of carlson et al 1986 and the empirical velocity porosity function of raymer et al 1980 supports the conclusion that pelagic carbonate sediments on oceanic plateaus and rises have unique acoustic properties primarily arising from the presence of intraparticle porosity and should not be grouped with other oceanic lithologies in acoustic modeling studies

physical property changes as a monitor of pelagic carbonate diagenesis an empirically derived diagenetic model for atlantic ocean basins a new physical model of carbonate diagenesis has been derived based on physical property measurements from 81 dsdp odp deep sea drilling project ocean drilling project drill sites in the atlantic ocean changing depth gradients of porosity bulk density p wave velocity vertical and horizontal and acoustic impedance characterize five successive diagenetic stages 1 compaction of ooze 2 breakage and dissolution of fossil tests 3 formation of chalk through precipitation of calcite 4 cementation and 5 compaction of calcite crystals age depth information from the drill sites was used to calculate the average duration of these processes in atlantic ocean basins the model can predict carbonate sediment physical properties down to a burial depth of 1000 m the model is presented for both lab and in situ conditions and thus can serve as a standard for comparison with lab log and seismic measurements an acoustic impedance vs age curve derived from the model allows estimation of the initial and present day diagenetic potential of carbonate sediments and chalk reservoirs

changes in attenuation with depth in an ocean carbonate section ocean drilling program sites 806 and 807 ontong java plateau changes of in situ seismic attenuation with depth are estimated from full waveform acoustic logs in a soft formation rock with shear velocity less than borehole fluid velocity the relative attenuation qp 1 is computed from the variation with depth of the p wave amplitude spectrum of a single source receiver pair the method is applicable when unknown source and receiver responses of the sonic tool make other methods difficult to apply tests with synthetic data generated by a full waveform method verify that in a soft formation the decay of the p wave amplitude spectrum depends mainly on attenuation the method is applied to ocean drilling program data from holes 806b and 807a on the ontong java plateau in the western pacific ocean four attenuation logs were computed independently using data from four source receiver pairs agreement of the four logs at each site and agreement of results from the two sites suggest that the method is robust and practical the attenuation logs show a maximum attenuation between 300 and 500 m below the seafloor they agree well with compilations of high frequency attenuation versus porosity and frequency in marine sediments but are somewhat greater than results from seismic experiments possibly owing to the presence of sedimentary microbeds and the three decade difference between the seismic and sonic frequency bands

late quaternary lacustrine history and paleoclimatic significance of pluvial lake cochise southeastern arizona abstract during the latest quaternary freshwater pluvial lakes intermittently formed in the topographically closed willcox basin arizona a lacustrine sequence of six separate high stands of lake cochise is documented by stratigraphic studies 19 radiocarbon ages and supplementary evidence two stands of pluvial lake cochise older than 14 000 yr b p reached elevations above 1290 m the prominent 1274 m shoreline of lake cochise which circumscribes the basin was largely created during a high stand between 13 750 and 13 400 yr b p during the holocene water filled the willcox basin three times to an elevation slightly below the crest of the 1274 m shoreline this occurred once during the early holocene around or before 8900 yr b p and twice during the later part of the middle holocene since the middle holocene only shallow ephemeral lakes have occupied the deflated central portion of ancient lake cochise a depression known as the willcox playa the lacustrine sequence of lake cochise provides an independent evaluation of late quaternary paleoclimatic reconstructions for southern arizona and the american southwest

infra red stimulated luminescence ages from aeolian sand and alluvial fan deposits from the eastern mojave desert california abstract infra red stimulated luminescence irsl from coarse grained 180 212 m potassium rich feldspars has been used to date deposits associated with the western piedmont of the providence mountains in the eastern mojave desert these deposits consist of alluvial fans aeolian sand which exists in the form of lenses within the fan matrices and sand from the kelso dune field which abuts the distal end of the fan sequence deposition and subsequent stabilisation of these sand units appears to have occurred in both aird and intermittent climates associated with pluvial phases during the holocene and late pleistocene ages of 6600 870 and 7840 1790 years were obtained from dune sand bracketing the mazama ash at skull creek dunes oregon giving an independent age control on the single aliquot irsl method which was used on the mojave samples

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

interpretations and common challenges of aeolian records from north american dune fields abstract geomorphic and chronologic data for dune fields are evaluated for three contrasting areas of north america 1 the prairie parkland and boreal ecozones of the northern great plains in canada 2 the central great plains of the usa and 3 the deserts of southwestern usa and northern mexico luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply availability and mobility dune fields in the northern great plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16 11 ka subsequent aeolian deposition occurred in parkland and prairie dune fields as a result of mid holocene 8 5 ka and late holocene despite spatial and temporal gaps in chronometric data as a result of sampling biases the record from north american dune fields indicates the strong influence of sediment supply on dune construction with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre existing sediment

the determination of statistical and deterministic hydrological landslide triggering thresholds hydrological landslide triggering thresholds separate combinations of daily and antecedent rainfall or of rainfall intensity and duration that triggered landslides from those that failed to trigger landslides they are required for the development of landslide early warning systems when a large data set on rainfall and landslide occurrence is available hydrological triggering thresholds are determined in a statistical way when the data on landslide occurrence is limited deterministic models have to be used for shallow landslides directly triggered by percolating rainfall triggering thresholds can be established by means of one dimensional hydrological models linked to the infinite slope model in the case of relatively deep landslides located in topographic hollows and triggered by a slow accumulation of water at the soil bedrock contact simple correlations between landslide occurrence and rainfall can no longer be established therefore real time failure probabilities have to be determined using hydrological catchment models in combination with the infinite slope model

modelling of porosity evolution and mechanical compaction of calcareous sediments a continuum mechanics model for the gravitational compaction of sediments is derived by assuming that the sediments are normally pressured and in a one dimensional state of stress sediment strength is characterized in terms of effective stress laws adopted from soil mechanics the model is a relatively simple mathematical formula that gives the porosity as a function of burial depth the shape of the porosity profile is controlled by two mechanical parameters the compression index and the void ratio at an effective stress of 100 kpa the model was verified by analysing the porosity depth data of oozes and chalk from the ontong java plateau gathered during leg 130 of the ocean drilling program the mechanical parameters of the sediments were estimated using a least squares method to fit the theoretical profile to the porosity data the theoretical profile described accurately the ooze porosity data over depth ranges of 100 m or more however over smaller length scales of 10 50 m there were systematic deviations between the theoretical porosity values and the ooze porosity data the porosity deviations correlated with variations in the mean grain size of the sediments due in part to changes in the foraminifera abundance in the case of the oozes the estimated mechanical parameters were consistent with published values obtained from one dimensional compression tests in contrast the estimated mechanical properties for the chalks differed from published values the chalk porosities were lower than could be explained by mechanical compaction this explanation is supported by the compressional p wave velocity data in the chalk sections the p wave velocity increases more rapidly with burial depth than it does in the ooze sections suggesting that sediment elastic properties are increasing due to interparticle binding

gis modelling of slope stability in phewa tal watershed nepal abstract hazards are an inherent but dangerous and costly element of mountainous environments conventional maps of mountain hazards provide useful inventories of hazardous sites but provide little insight into the operation of the hazards furthermore this approach tends to rely heavily on subjective interpretation of the landscape which means that the results can not be replicated or transferred to other areas thus alternative approaches employing the quantitative capabilities of geographic information systems gis to model and predict slope stability are receiving increasing attention this paper reports on the use of a diverse gis database compiled primarily from existing maps and aerial photographs to construct a regional model of slope stability in phewa tal watershed nepal an integral part of the research was to explore an alternative approach to the commonly used grid cell approach by employing geomorphometrically significant terrain units the terrain units employed were created by generating line networks representing local maxima and minima extracted from elevation and curvature surfaces one of the chief benefits of applying gis technology in this research was the ability to georeference all of the attribute data to these terrain units in doing so it allowed the database to be exported into an external statistical package where the terrain units could be statistically explored as the basic analytical unit the application of a variety of statistical techniques resulted in logistic regression being selected as the most useful logistic regression successfully predicted terrain units as being either stable or unstable at a rate of approximately 90 concordance with a conventionally produced map of slope stability the statistical probabilities of terrain unit stability were imported back into the gis to produce a map of predicted slope stability that compared well with the conventional map of slope stability the findings of this research suggest that the use of geomorphometrically significant terrain units extracted from a digital elevation model dem are an efficient alternative to approaches using regular grid cells in particular the terrain units facilitated the use of logistic regression and significantly decreased the amount of computing costs finally this research also suggests that important information can be gathered from existing information sources such as maps aerial photographs and written documents thereby limiting the need for costly and time consuming field work at the reconnaissance level based on this latter finding other information sources such as satellite imagery should be examined

changes in land cover and shallow landslide activity a case study in the spanish pyrenees the pyrenees like many other mountain areas in europe have experienced depopulation and land abandonment during the 20th century this has encouraged vegetation recovery in formerly occupied areas including reforestation to promote woodland the objective of this study is to analyse the effects of these changes on shallow landsliding a process responsible for erosion and land degradation in many mountain areas a sequence of aerial images reveals a slight decrease in the landslide occurrence rate in the last half of the 20th century and a parallel increase in the landslide extinction rate i e the rate at which evidence of landslide activity is removed by vegetation colonisation a logistic regression routine was used to assess the influence of land use and vegetation recovery in the occurrence of shallow landslides the result shows that the former arable fields on the valley slopes still facilitate landsliding even after land abandonment and revegetation by shrubs or trees a shift in the topographic location of landslides was also detected pointing to an increased importance of water redistribution in the slopes after prolonged rainfall periods

a revised chronology for aeolian activity in subarctic fennoscandia during the holocene detailed sedimentological studies and parallel sampling for 14c and infra red stimulated luminescence age assays were undertaken at six sites lying beyond and below the tree line with the objective of establishing the historical development of aeolian landforms in lapland the main issues were a the timing of dune activity and processes of stabilization b the specific processes responsible for the past and contemporary activity new data indicate that many of the primary dunes were active for several millennia after deglaciation diachronous stabilization at both local and regional scales appears likely initial stabilization occurred in local interdune areas and where regional dune fields were colonized by pine generally before 7 ka local large dunes and some regional dunefields only became stable around 4 3 ka when the regional groundwater table rose and late pine colonization was possible the latest episode of aeolian activity dates from ad 1100 1650 across the area a unique deflation trigg

on the formation of sand ramps a case study from the mojave desert sand ramps are dune scale sedimentary accumulations found at mountain fronts and consist of a combination of aeolian sands and the deposits of other geomorphological processes associated with hillslope and fluvial activity their complexity and their construction by wind water and mass movement means that sand ramps potentially hold a very rich store of palaeoenvironmental information however before this potential can be realised a full understanding of their formation is necessary this paper aims to provide a better understanding of the principal factors influencing the development of sand ramps it reviews the stratigraphic chronometric and sedimentological evidence relating to the past development of sand ramps focussing particularly on soldier mountain sand ramp in the mojave desert as well as using observations of the modern movement of slope material to elucidate the formation of stone horizons within sand ramps findings show that sand ramps cannot easily be interpreted in terms of a simple model of fluctuating palaeoenvironmental phases from aeolian dominated to soil fluvial dominated episodes they accumulate quickly perhaps in 5 ka probably in a single phase before becoming relict based on the evidence from soldier mountain they appear strongly controlled by a window of opportunity when sediment supply is plentiful and cease to develop when this sediment supply diminishes and or the accommodation space is filled up contemporary observations of stone movement both on rock and sandy sloping surfaces in the mojave region indicate movement rates in the order of 0 6 and 11 mm yr 1 which is insufficiently fast to explain how stone horizons could have been moved across and been incorporated into sand ramps on multiple occasions stone horizons found within the aeolian sediments lack evidence for soil development and are interpreted as very short term events in which small streams moved and splayed discontinuous stone horizons across the sand ramp surface before aeolian deposition resumed surface stone horizons may form by creep from mountain slope sources across sand ramps but require enhanced speed compared to measured rates of runoff creep we propose the mechanism of fluvio aeolian creep our study suggests that current models of alternating aeolian and colluvial deposition within sand ramps their palaeoenvironmental significance and indeed how sand ramps are distinguished from other dune forms require amendment

probabilistic landslide hazard assessment at the basin scale abstract we propose a probabilistic model to determine landslide hazard at the basin scale the model predicts where landslides will occur how frequently they will occur and how large they will be we test the model in the staffora river basin in the northern apennines italy for the study area we prepare a multi temporal inventory map through the interpretation of multiple sets of aerial photographs taken between 1955 and 1999 we partition the basin into 2243 geo morpho hydrological units and obtain the probability of spatial occurrence of landslides by discriminant analysis of thematic variables including morphological lithological structural and land use for each mapping unit we obtain the landslide recurrence by dividing the total number of landslide events inventoried in the unit by the time span of the investigated period assuming that landslide recurrence will remain the same in the future and adopting a poisson probability model we determine the exceedance probability of having one or more landslides in each mapping unit for different periods we obtain the probability of landslide size by analysing the frequency area statistics of landslides obtained from the multi temporal inventory map assuming independence we obtain a quantitative estimate of landslide hazard for each mapping unit as the joint probability of landslide size of landslide temporal occurrence and of landslide spatial occurrence

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

the application of gis based logistic regression for landslide susceptibility mapping in the kakuda yahiko mountains central japan as a first step forward in regional hazard management multivariate statistical analysis in the form of logistic regression was used to produce a landslide susceptibility map in the kakuda yahiko mountains of central japan there are different methods to prepare landslide susceptibility maps the use of logistic regression in this study stemmed not only from the fact that this approach relaxes the strict assumptions required by other multivariate statistical methods but also to demonstrate that it can be combined with bivariate statistical analyses bsa to simplify the interpretation of the model obtained at the end in susceptibility mapping the use of logistic regression is to find the best fitting function to describe the relationship between the presence or absence of landslides dependent variable and a set of independent parameters such as slope angle and lithology here an inventory map of 87 landslides was used to produce a dependent variable which takes a value of 0 for the absence and 1 for the presence of slope failures lithology bed rock slope relationship lineaments slope gradient aspect elevation and road network were taken as independent parameters the effect of each parameter on landslide occurrence was assessed from the corresponding coefficient that appears in the logistic regression function the interpretations of the coefficients showed that road network plays a major role in determining landslide occurrence and distribution among the geomorphological parameters aspect and slope gradient have a more significant contribution than elevation although field observations showed that the latter is a good estimator of the approximate location of slope cuts using a predicted map of probability the study area was classified into five categories of landslide susceptibility extremely low very low low medium and high the medium and high susceptibility zones make up 8 87 of the total study area and involve mid altitude slopes in the eastern part of kakuda mountain and the central and southern parts of yahiko mountain

comparison of satellite and air photo based landslide susceptibility maps landslide susceptibility maps can be prepared in a variety of ways many geoscientists favour the use of an overlay model approach in which several map layers are combined by some arithmetic rules to determine the potential for sliding in an area or region the resulting susceptibility maps although based on a subjective weighting of relevant factors can often be of high accuracy and utility in order to obtain the relevant input data for this type of analysis remotely sensed data are often used to date susceptibility mapping just as the mapping of historic and individual landslides has tended to require higher resolution imagery this has somewhat limited the application of landslide susceptibility mapping while high resolution air photo or satellite imagery is superior to lower resolution imagery for the purpose of mapping of historic and individual landslides such higher levels of resolution may not be required for the development of landslide susceptibility maps in order to determine if medium resolution satellite imagery such as spot or aster could provide the needed data for landslide susceptibility mapping a comparison was undertaken of landslide susceptibility model output resulting from the use of stereo napp aerial photography versus the use of data obtained from stereo spot imagery the test area selected for this study consisted of two watersheds pena canyon and big rock canyon situated west of santa monica california usa along the pacific coast highway both watersheds have a long and well documented history of landslide activity and sufficient geologic variability and complexity to provide a good test site the specific overlay model used in this evaluation required input data consistent with the needs of many other models of this type the model output derived from the two different data sources and presented here in the form of susceptibility maps were virtually identical statistical and difference analysis confirmed that both methods of obtaining input data provide similar results and successfully identified landslide prone areas these results suggest that satellite imagery in this instance spot images could potentially be used in lieu of conventional air photos to evaluate landslide susceptibility in many situations especially in the case of remote locations and or developing countries this capability should result in substantial savings in terms of time financial resources and overall viability

acoustic and mechanical properties of nankai accretionary prism core samples we studied undeformed sediment and accreted strata recently recovered by ocean drilling program integrated ocean drilling program odp iodp drilling in nankai trough convergent margin to unravel the changes in physical properties from initial deposition to incipient deformation we have derived acoustic vp and mechanical uniaxial poroelastic compliance compaction amplitude properties of samples from various drill sites along the muroto odp 1173 and kii transects iodp c0001 c0002 c0006 and c0007 from isotropic loading tests where confining and pore pressure were independently applied we quantified the dependence of vp on both effective peff and confining pc pressure which can be used to correct atmospheric pressure measurements of vp experimental vp obtained on core samples extrapolated to in situ conditions are slightly higher than logging derived velocities which can be attributed either to velocity dispersion or to the effect of large scale faults and weak zones on waves with longer wavelength in the high porosity 30 60 tested sediments velocities are controlled at first order by porosity and not by lithology which is in agreement with our static measurements of drained framework incompressibility much smaller than fluid incompressibility rather than framework incompressibility shear modulus is probably the second order control on vp accounting for most of the difference between actual vp and the prediction by wood s 1941 suspension model we also quantified the mechanical state of nankai samples in terms of anisotropy diagenesis and consolidation both acoustic and mechanical parameters reveal similar values in vertical and horizontal directions attesting to the very low anisotropy of the tested material when considering the porous samples of the upper shikoku basin sediments site 1173 as examples of diagenetically cemented material several mechanical and acoustic attributes appeared as reliable experimental indicators of the presence of intergrain cementation we also detected incipient cementation in samples from iodp site c0001 accretionary prism unit in terms of consolidation we distinguished two classes of material response shallow deformable samples and deep hardly deformable ones based on the amount of compaction upon application of a peff large with respect to the inferred in situ value with a transition that might be related to a critical porosity

late quaternary stratigraphy and luminescence geochronology of the northeastern mojave desert abstract the chronology of the holocene and late pleistocene deposits of the northeastern mojave desert have been largely obtained using radiocarbon ages our study refines and extends this framework using optically stimulated luminescence osl to date deposits from valjean valley silurian lake playa red pass and california valley of particular interest are eolian fine silts incorporated in ground water discharge gwd deposits bracketed at 185 140 and 20 50 ka alluvial fan deposits proved amenable for osl by dating both eolian sand lenses and reworked eolian sand in a matrix of gravel that occurs within the fan stratigraphy lacustrine sand in spits and bars also yielded acceptable osl ages these osl ages fill gaps in the geochronology of desert deposits which can provide data relevant to understanding the responses of several depositional systems to regional changes in climate this study identifies the most promising deposits for future luminescence dating and suggests that for several regions of the mojave desert sediments from previously undated landforms can be more accurately placed within correct geologic map units

late quaternary arid humid cycles in the mojave desert and western great basin of north america abstract this paper discusses the late quaternary environmental changes that occurred in the drylands of western north america with particular emphasis on the aeolian lacustrine record from the mojave desert the basin and range province which includes the great basin and the mojave sonoran and chihuahuan deserts the primary physiographic region within the north american arid zone is characterized by a wide variety of landforms within a predominantly endoreic block faulted tectonic setting in these closed drainage basins lacustrine and aeolian geomorphic features and sediments have provided some of the best records for deciphering environmental changes about 100 of the basins contained lakes during the last glacial maximum lgm at larger temporal scales milankovitch dansgaard oeschger cycles lake levels seem to be well correlated with large scale atmospheric circulation controls such as the higher lake stands associated with wetter than present conditions in the southwestern drylands during the lgm on the other hand aeolian deposition was highly episodic during late quaternary time and is believed to be largely controlled by variations in sediment supply and production storage and transport capacity

physically based modelling of shallow landslide sediment yield at a catchment scale a shallow landslide erosion and sediment yield component applicable at the basin scale has been incorporated into the physically based spatially distributed hydrological and sediment transport modelling system shetran the component determines when and where landslides occur in a basin in response to time varying rainfall and snowmelt the volume of material eroded and released for onward transport and the impact on basin sediment yield derived relationships are used to link the shetran grid resolution up to 1 km at which the basin hydrology and final sediment yield is modelled to a subgrid resolution typically around 10 100 m at which landslide occurrence and erosion is modelled the subgrid discretization landslide susceptibility and potential landslide impact are determined in advance using a geographic information system gis with shetran then providing information on temporal variation in the factors controlling landsliding the ability to simulate landslide sediment yield is demonstrated by a hypothetical application based on a catchment in scotland

a new seismic stratigraphy in the indian atlantic ocean gateway resembles major paleo oceanographic changes of the last 7 ma the exchange of water masses between the indian ocean and the atlantic constitutes an integral interocean link in the global thermohaline circulation long term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late miocene onward here we present results from international ocean discovery program site u1475 agulhas plateau located over a sediment drift proximal to the entrance of north atlantic deep water into the southern ocean and south indian ocean site u1475 comprises a complete carbonate rich stratigraphic section of the last 7 ma that provides an archive of climate induced variations in ocean circulation six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time the formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy prominent reflectors are related to late pleistocene glacial interglacial variability the middle and early pleistocene transitions and the onset of the northern hemisphere glaciation a peculiar early pliocene interval 5 3 4 0 ma bounded by two reflectors is characterized by fourfold elevated sedimentation rates 10 cm kyr and the occurrence of sediment waves we argue that this enhanced sediment transport to the agulhas plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of north atlantic deep water

optical dating of holocene dune sands in the ferris dune field wyoming abstract optical dating of late quaternary quartz dune sands from the clear creek portion of ferris dune field wyoming demonstrates the considerable potential of the technique as a chronostratigraphic tool a sequence of radiocarbon dated holocene interdune strata permit optical dating of the intercalated dune sand to be tested the concordance is good the optical dates for the aeolian deposits not datable by radiocarbon suggest that aeolian sedimentation at clear creek peaked during two relatively short phases at ca 8500 and 4000 yr b p the dates indicate that aeolian accumulation maxima at least in the clear creek area may not be synchronous with previously defined phases of marked aridity

resistance to shallow landslide failure through root derived cohesion in east coast hill country soils north island new zealand measured shear strength cohesion and friction of airfall derived east coast hill country regolith is insufficient for the maintenance of existing regolith depth slope angle relationships in the catchment of lake waikopiro in northern hawke s bay new zealand if these regoliths are attributed with an additional increment of cohesion derived mechanically from a turf mat membrane existing depth slope angle distributions are explicable sites where failure has occurred have been measured and back analysis used to derive a range of values for additional mechanical cohesion values are in the range 0 2 7 6 kpa consistent with earlier findings this range is narrowed further to 0 7 6 9 kpa with assumptions regarding soil moisture status at failure copyright 1999 john wiley sons ltd

multifractal and entropic properties of landslides in japan landslide distributions in two major areas of northern japan tohoku and hokkaido are analysed for multifractal properties for the latter data set also the multifractal spectrum for the spatial landslide size distribution is determined and compared to the probability distribution it is concluded that the fields possess definite multifractal character this finding is supported by the known multifractality of the main triggering processes rain and earthquakes further support comes from a configuration entropy analysis which is found to be a useful complimentary tool to multifractal analysis models leading to multifractality are briefly reviewed careful attention is paid to the algorithms used and to the verification of the numerical results some general suggestions concerning numerical methods are made

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

luminescence dating of late quaternary aeolian deposits at dale lake and cronese mountains mojave desert california abstract relict aeolian deposits and landforms that can provide important information on the timing geographical extent and intensity of periods of aeolian sand accumulation are widespread in the mojave desert california the pleistocene part of the record is mostly undated the stratigraphy and sedimentology of sites near dale lake dale lake sand ramp and the cronese mountains cat dune were studied and luminescence dating techniques used to try to establish a chronological framework for the deposits the dating of these sites proved difficult with major disparities between the results of quartz and feldspar thermoluminescence tl dating particularly where the sediments comprised a mixture of aeolian and colluvial meterial however initial results based on quartz tl and feldspar infra red stimulated luminescence dating indicate the existence of two main periods of late pleistocene aeolian deposition between 35 to 25 ka and 15 to 10 ka

landslide zoning in a part of the garhwal himalayas the himalayas are undergoing constant rupturing in the thrust belt zone in the garhwal himalayas due to which earthquake and mass movement activity is triggered these processes of mass movement and landslides have been constantly modifying the landscape landslides are one of the indicators of the geomorphological modifications taking place in this active and fragile terrain this work is aimed at providing another example of landslide susceptibility mapping based on geological and geomorphological attributes the data collected from aerial photographs topographic sheets and the image suggests that there is a correlation between the distribution of landslides and some of the geological and geomorphological factors for example the distance from an active fault relative relief and slope parameters like factor of safety altitude relief slope and the distance from the fault lineament have been included in the study a rating system has been applied to the factors for arriving at a quantitative estimate of landslide susceptibility for each physiographic unit since terrain classification forms the foundation of this work the entire study can be grouped into two sequential activities 1 the terrain classification and 2 landslide susceptibility mapping the result is the landslide susceptibility zoning map presented the landslides have not been classified with respect to time and may represent the final result of the on going geological geomorphological and seismic activity since the holocene period or late pleistocene time when the glaciers retreated