development of partial rock veneers by root throw in a subalpine setting rock veneers stabilize hillslope surfaces occur especially in areas of immature soil and form through a variety of process sets that includes root throw near westcliffe colorado usa data were collected from a 20 500 m transect on the east slope of the sangre de cristo mountains ages of pit mound complexes with rock fragments exposed at the surface by root throw ranged from recent freshly toppled tree to unknown complete tree decay calculations based on dimensions of the pit mound complexes estimated time of tree toppling sizes of exposed rock fragments and percentage rock covers at pit mound complexes as well as within the transect area indicate that recent rates of root throw have resulted in only partial rock veneering since late pleistocene deglaciation weathering of rock fragments prevents development of an extensive rock veneer and causes a balance achieved within an estimated 700 years between the rates of rock fragment exposure by root throw and clast disintegration by chemical reduction the estimated rate of rock fragment reduction accounts for part of the fluvial sediment yields observed for forested subalpine areas of western north america copyright 2005 john wiley sons ltd

shallow perched groundwater a flux of deep co and near surface water rock interaction in northeastern jordan an example of positive feedback and darwin s warm little pond abstract darwin s warm little pond where he envisioned life began was perhaps metaphorical however it included the notion of separation just as the galapagos islands are separated from mainland south america we have studied a location where simple life flourishes far from other abundant life i e a permanently damp surficial zone that is surrounded by stark desert in ne jordan ne jordan is a young basaltic plateau with fresh outcrops however a positive feedback process has produced local weathering at biyar el ghussein in the tulul al ashaqif area calcite smectites and goethite occur with parent minerals water that is inducing this weathering has come from rainfall but the isotopic composition of abundant carbonate veins reveals a deep source i e volcanogenic co 2 a local coincidence of groundwater and rising co 2 is inducing a positive feedback process enhancing a weakly perched water table through weathering of basalt additional perched water dissolves more volcanogenic co 2 accelerating decomposition of the basalt and enlarging the aquiclude

soil geomorphic research a selective overview abstract much soil geomorphologic research involves tracking the development of soils with time otherwise known as soil chronosequences most of these have been undertaken on landforms underlain by quaternary depsits of varying ages in general there is a predictable variation in both soil horizon sequence and amounts of constituents such as clay fe and caco 3 with time the rate at which these constituents accumulate in the soil is a function of parent material bioclimate and atmospheric dust influx and because of the latter soils in aridic regions can form at rapid rates profile properties can be used to estimate the ages of deposits and faulting events but the error on the estimated age can be 50 or greater the position of salt accumulations in soil profiles is one of the best indications of climatic change and these can be modelled to compare with various climatic parameters present and past profile characteristics due to pedogenic thresholds however can mimic those due to climatic change so close dating is necessary to differentiate the effects of both soil geomorphic data are essential to understand the origin of ancient paleosols in the sedimentary rock records but a major problem still is one of recognition of these features as soils and to separate the effects of pedogenesis from those of diagenesis

mcget a rapid image based method to determine the morphological characteristics of gravels on the gobi desert surface abstract the relationship between morphological characteristics e g gravel size coverage angularity and orientation and local geomorphic features e g slope gradient and aspect of desert has been used to explore the evolution process of gobi desert conventional quantification methods are time consuming inefficient and even prove impossible to determine the characteristics of large numbers of gravels we propose a rapid image based method to obtain the morphological characteristics of gravels on the gobi desert surface which is called the morphological characteristics gained effectively technique mcget the image of the gobi desert surface was classified into gravel clusters and background by a machine learning classification and regression tree cart algorithm then gravel clusters were segmented into individual gravel clasts by separating objects in images using a watershed segmentation algorithm thirdly gravel coverage diameter aspect ratio and orientation were calculated based on the basic principles of 2d computer graphics we validated this method with two independent datasets in which the gravel morphological characteristics were obtained from 2728 gravels measured in the field and 7422 gravels measured by manual digitization finally we applied mcget to derive the spatial variation of gravel morphology on the gobi desert along an alluvial proluvial fan located in hami xinjiang china the validated results show that the mean gravel diameter measured in the field agreed well with that calculated by mcget for large gravels r2 0 89 p

evidence suggesting that methods of rock varnish cation ratio dating are neither comparable nor consistently reliable abstract using samples from a prehistoric quarry site in the mojave desert we tested and compared the two principal methods of rock varnish cation ratio dating analysis of rock varnish scrapings r i dorn 1983 quaternary research 20 49 73 and 1989 physical geography 13 559 596 and analysis of rock varnish in situ c d harrington and j w whitney 1987 geology 15 967 970 because we found no consistent relationship between the varnish cation ratio k ca ti and the relative age of the varnish neither method could be used to cation ratio date the underlying chert artifacts moreover in situ analyses yielded systematically higher cation ratios and lower ti abundances than bulk analyses of scraped varnish or microprobe analyses of varnish in cross section our results when considered along with other recently published evidence indicate that these two methods of varnish chemical analysis and cation ratio dating may not be comparable nor consistently reliable chronometers

preferential dust sources a geomorphological classification designed for use in global dust cycle models received 11 april 2011 revised 28 september 2011 accepted 4 october 2011 published 24 december 2011 1 we present a simple theoretical land surface classification that can be used to determine the location and temporal behavior of preferential sources of terrestrial dust emissions the classification also provides information about the likely nature of the sediments their erodibility and the likelihood that they will generate emissions under given conditions the scheme is based on the dual notions of geomorphic type and connectivity between geomorphic units we demonstrate that the scheme can be used to map potential modern day dust sources in the chihuahuan desert the lake eyre basin and the taklamakan through comparison with observed dust emissions we show that the scheme provides a reasonable prediction of areas of emission in the chihuahuan desert and in the lake eyre basin the classification is also applied to point source data from the western sahara to enable comparison of the relative importance of different land surfaces for dust emissions we indicate how the scheme could be used to provide an improved characterization of preferential dust sources in global dust cycle models

mapping north african landforms using continental scale unmixing of modis imagery we describe the production of a landform map of north africa utilizing moderate resolution satellite imagery and a methodology that is applicable for sub continental to global scale landform mapping a mosaic of moderate resolution imaging spectroradiometer modis apparent surface reflectance imagery was compiled for africa north of 10 n landform image endmembers were chosen to characterize ten different types of vegetated and unvegetated desert surfaces alluvial complexes dunes dry and ephemeral lakes open water basaltic volcanoes and flows mountains regs stripped low angle bedrock surfaces sand sheets and sahelian vegetation multiple endmember spectral mixture analysis mesma was applied to the modis mosaic to estimate landform and vegetation endmember fractions the major landform in each modis pixel was identified based on the majority endmember fraction in two or three endmember models accuracy assessment was conducted using two data sources the historic landform map of north africa raisz e 1952 landform map of north africa environmental protection branch office of the quartermaster general and landsat thematic mapper tm data comparison with the raisz landform map gave an overall classification accuracy of 54 with significant confusion between alluvial surfaces and regs and between sandy and clayey surfaces and dunes a second validation using 20 landsat images in a stratified sampling scheme gave a classification accuracy of 70 with confusion between dunes and sand sheets both accuracy assessment schemes indicated difficulty in vegetation classification at the margin of the sahel a comparison with minimum distance and maximum likelihood supervised classifications found that the mesma approach produced significantly higher classification accuracies this digital landform map is of sufficiently high quality to form the basis for geomorphic studies including parameterization of the surface in global and regional dust models

geochemical isotopic and mineralogical constraints on atmospheric deposition in the hyper arid atacama desert chile abstract modern atmospheric deposition across the atacama was collected by an array of dust traps that stretched from the pacific coast to the andean altiplano and the material was analyzed for its geochemical mass and isotopic composition the coastal trap had the second highest insoluble mineral particle and highest soluble salt deposition rates due to significant inputs from the morro mejillones range and the pacific ocean respectively the andean trap had the highest insoluble mineral particle deposition owing to transport of weathered material but the lowest deposition rate of soluble salts due to its distance from the ocean and anthropogenic sources the removal of oceanic material was effective by the coastal mountains while the westward transport of the andean material was determined to be minimal the atmospheric deposition in the inland traps was mainly from the local entrainment of surface material inland anthropogenic emissions and transport of marine aerosols the nitrate isotopes 15 n and 17 o suggested that no x sources and no 3 chemistry shifted along the west east transect and were greatly impacted by anthropogenic emissions with soil no 3 being a minor source of deposited nitrogen

estimating the age of desert alluvial surfaces with spaceborne radar data abstract we present a new dating approach for desert alluvial surfaces that utilizes radar image data to obtain regional scale correlations between dated surfaces and surfaces of unknown ages the study was carried out along the arava segment of the dead sea transform north of the gulf of elat aqaba using advanced land observation satellite alos phased array type l band synthetic aperture radar palsar data with 6 12 m pixel resolutions nineteen independently dated quaternary morphostratigraphic alluvial units 5 to 1910 ka from eight different sites with variable lithologies carbonate magmatic chert were examined in order to develop test and validate the proposed approach expanding on previous studies that established the characteristic smoothing of desert alluvial surface through time and the capability of measuring such roughness variations with radar we employed a pixel aggregation approach that yielded a robust r 2 0 95 power law relation between the average radar backscatter value from the surface ar and the abandonment age t of the unit as measured with independent methods such as luminescence and or cosmogenic radionuclide dating we found that 1 this ar t correlation can be inverted to obtain calibrated radar based t estimates as old as 1 5 ma with 35 uncertainty 2 alos palsar 6 m pixel images acquired at incidence angles of 34 38 yielded optimal results 3 a sample of at least 70 contiguous radar pixels was required to capture the natural roughness variability of the surfaces examined and 4 surface lithology did not exert a primary effect on t inversions validation experiments yielded radar based ages of 3 1 91 32 484 169 and 1604 561 ka that compare to holocene 56 14 540 60 and 1590 250 ka ages previously determined for the same surfaces respectively we propose that with region specific calibrations spaceborne radar data can be used to quantitatively estimate the age of abandoned alluvial units across regional scales

cosmogenic 3he exposure ages of pleistocene debris flows and desert pavements in capitol reef national park utah abstract the quaternary history of the capitol reef area utah is closely linked to the basaltic andesite boulder deposits that cover much of the landscape understanding the age and mode of emplacement of these deposits is crucial to deciphering the quaternary evolution of this part of the colorado plateau using cosmogenic 3 he exposure age dating we obtained apparent exposure ages for several key deposits in the capitol reef area coarse boulder diamicts capping the johnson mesa and carcass creek terraces are not associated with the bull lake glaciation as previously thought but were deposited 180 15 to 205 17 ka minimum age and are the result of debris flow deposition desert pavements on the johnson mesa surface give exposure ranging from 97 8 to 159 14 ka and are 34 96 kyears younger than the boulder exposure ages the offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition incision rates for the capitol reef reach of the fremont river calculated from the boulder exposure ages range from 0 40 to 0 43 m kyear 1 maximum rates and are some of the highest on the colorado plateau

hydrologic variability and the onset of modern el nino southern oscillation a 19 250 year record from lake elsinore southern california there are very few terrestrial palaeoclimate archives spanning the last glacial maximum through the holocene from coastal southern california yet knowledge of past climate dynamics is critical for assessing present and future constraints on the region s dwindling freshwater resources we present initial results from two drill cores extracted from the present day edge of lake elsinore southern california s largest natural lake using a multiproxy approach including lithologic description mass magnetic susceptibility loi 550 c total organic matter and loi 950 c total carbonate we infer first order long term climate change over the past 19 250 calendar years furthermore we suggest possible first order forcing mechanisms that drive this change which include presence absence of continental ice sheets insolation and complex ocean atmosphere interactions our results indicate four distinct millennial scale climate modes over the past 19 250 calendar years these modes include a wet last glacial maximum 19 250 17 120 cal yr bp a relatively dry late glacial holocene transition 17 120 9450 cal yr bp a wet early holocene 9450 7670 cal yr bp and a highly variable mid to late holocene climate i e alternating wet dry cycles 7670 cal yr bp present we attribute the mid to late holocene climate interval to the onset of el nino southern oscillation ca 7000 cal yr bp and a more vigorous hydrologic system these results are supported by a variety of regional terrestrial and marine palaeoclimate archives copyright 2005 john wiley sons ltd

effect of rock fragment eccentricity on eolian deposition of atmospheric dust abstract the effect of rock fragment eccentricity on the deposition of airborne dust was examined in a wind tunnel eccentricity was defined as the ratioa b wherea is the longest andb the intermediate axis of the rock fragments the effect of eccentricity on the deposition of dust on the pebbles on the deposition of dust between and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately and this for different values of pebble size pebble flattening cover density and wind speed the more pebbles are elongated the larger dust deposition on them will be this effect is more pronounced as pebbles become larger as they become less flattened and as wind speed increases but no correlation is observed with cover density it also holds that the more pebbles are elongated the less dust settles between and underneath them this effect is more pronounced as pebbles become smaller and cover density becomes larger but there is no relationship with pebble flattening whether or not there is a relationship with wind speed is unclear pebble eccentricity indirectly influences total dust deposition on a pebble field since it determines whether or not and to what extent total dust deposition will be a function of pebble size for circular pebbles total dust deposition is independent of pebble size but once pebbles become elongated total dust deposition will be smaller on pebble fields composed of small pebbles than on pebble fields composed of large pebbles it was also demonstrated that the more pebbles are elongated the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation plays a primary role in the deposition of dust on a rock fragment field since it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles highly elongated pebbles oriented parallel to the wind catch much more dust also per unit surface than circular pebbles the surface of which is largely located in a zone of very low deposition dust deposition density on highly elongated pebbles normal to the wind on the contrary is equal to dust deposition on circular pebbles it should be noted that all data in this study refer to initial dust deposition not accumulation since only wind velocities below the dust deflation threshold were tested

geomorphic processes and remote sensing signatures of alluvial fans in the kun lun mountains china the timing of alluvial deposition in arid and semiarid areas is tied to land surface instability caused by regional climate changes the distribution pattern of dated deposits provides maps of regional land surface response to past climate change sensitivity to differences in surface roughness and composition makes remote sensing techniques useful for regional mapping of alluvial deposits radar images from the spaceborne radar laboratory and visible wavelength images from the french spot satellite were used to determine remote sensing signatures of alluvial fan units for an area in the kun lun mountains of northwestern china these data were combined with field observations to compare surface processes and their effects on remote sensing signatures in northwestern china and the southwestern united states geomorphic processes affecting alluvial fans in the two areas include aeolian deposition desert varnish and fluvial dissection however salt weathering is a much more important process in the kun lun than in the southwestern united states this slows the formation of desert varnish and prevents desert pavement from forming thus the kun lun signatures are indicative of the dominance of salt weathering while signatures from the southwestern united states are characteristic of the dominance of desert varnish and pavement processes remote sensing signatures are consistent enough in these two regions to be used for mapping fan units over large areas

soil carbonate genesis in the pinacate volcanic field northwestern sonora mexico uranium series methods were used to date and evaluate pedogenic caco3 genesis in the pinacate volcanic field northwestern sonora mexico soils are developed in eolian deposits on lava flows 230th234u dates of pedogenic carbonate are mininum soil ages because of 1 the time needed to yield clasts from flows and to accrete enough carbonate to sample 2 subsequent additions of uranium and 3 continued solution and reprecipitation of carbonate rinds k ar dates of basalt flows are maximum soil ages maximum and minimum rates of caco3 accumulation are calculated from the th u dates and k ar dates respectively the mean maximum rate is 0 13 g caco3 cm2 1000 yr and the mean minimum rate is 0 05 g caco3 cm2 1000 yr least squares regressions of pedogenic carbonate and clay content and of th u ages against k ar ages suggest additions to soils from atmospheric sources throughout the late quaternary morphology of pedogenic carbonate and laboratory data for soluble salts indicate that the climate of the pinacate has not changed significantly during the past 150 000 yr soil variability is influenced by proximity of the eolian source near the periphery of the pinacate carbonate and clay are evenly distributed throughout soil profiles within the volcanic field carbonate and clay are concentrated in soil horizons suggesting that additions from atmospheric sources are slow enough to allow translocation

a threshold in soil formation at earth s arid hyperarid transition the soils of the atacama desert in northern chile have long been known to contain large quantities of unusual salts yet the processes that form these soils are not yet fully understood we examined the morphology and geochemistry of soils on post miocene fans and stream terraces along a south to north 27 to 24 s rainfall transect that spans the arid to hyperarid transition 21 to 2 mm rain y 1 landform ages are 2 my based on cosmogenic radionuclide concentrations in surface boulders and ar isotopes in interbedded volcanic ash deposits near the driest site indicate a maximum age of 2 1 my a chemical mass balance analysis that explicitly accounts for atmospheric additions was used to quantify net changes in mass and volume as a function of rainfall in the arid 21 mm rain y 1 soil total mass loss to weathering of silicate alluvium and dust 1030 kg m 2 is offset by net addition of salts 170 kg m 2 the most hyperarid soil has accumulated 830 kg m 2 of atmospheric salts including 260 kg sulfate m 2 and 90 kg chloride m 2 resulting in unusually high volumetric expansion 120 for a soil of this age the composition of both airborne particles and atmospheric deposition in passive traps indicates that the geochemistry of the driest soil reflects accumulated atmospheric influxes coupled with limited in soil chemical transformation and loss long term rates of atmospheric solute addition were derived from the ion inventories in the driest soil divided by the landform age and compared to measured contemporary rates with decreasing rainfall the soil salt inventories increase and the retained salts are both more soluble and present at shallower depths all soils generally exhibit vertical variation in their chemistry suggesting slow and stochastic downward water movement and greater climate variability over the past 2 my than is reflected in recent 100 y rainfall averages the geochemistry of these soils shows that the transition from arid to hyperarid rainfall levels marks a fundamental geochemical threshold in wetter soils the rate and character of chemical weathering results in net mass loss and associated volumetric collapse after 105 to 106 years while continuous accumulation of atmospheric solutes in hyperarid soils over similar timescales results in dramatic volumetric expansion the specific geochemistry of hyperarid soils is a function of atmospheric sources and is expected to vary accordingly at other hyperarid sites this work identifies key processes in hyperarid soil formation that are likely to be independent of location and suggests that analogous processes may occur on mars

runoff generation rill erosion and time scales for hyper arid abandoned alluvial surfaces the negev desert israel abstract sequences of abandoned alluvial surfaces are ubiquitous desert landscapes considered as responding to quaternary timescale climatic fluctuations and tectonic activity the post depositional evolution surficial properties of these alluvial surfaces change with time a surface clast breakdown and development of desert pavement b dust and salts accumulation c reg gravelly desert soil evolution in the present study we focus on the hydrological response and the resulting erosional processes to these changes in surface properties over a sequence of late pleistocene holocene abandoned alluvial surfaces in nahal evrona catchment at the hyperarid southern arava valley north of the towns of eilat israel and aqaba jordan the methods used in the study are a simulated rainfall experiments to determine hydrological characteristics b terrestrial laser scanning tls to determine surface roughness c osl dating for the chronology d surface and soil descriptions and measurements and grain size analyses to determine texture of the uppermost av horizon of the reg soil e gis analysis of the new drainage network developing over the older abandoned alluvial surfaces the results show that with time roughness decreases infiltration decreases to about 8 9 relative to present rates point runoff generation increases 5 fold and as a result rill and gully erosion initiated finally leading to the destruction of the alluvial surface under the current hyper arid climate in the southern negev desert between 30 and 50 ka of surface weathering and soil development are required before significant runoff is generated and 100 ka until effective runoff initiates rill and gully erosion over these abandoned alluvial surfaces this local source runoff and gully erosion essentially destroys the alluvial surfaces in the southern arava valley within a period of 400 500 ka roughness extracted from spaceborne lidar scanning which is inversely related to surface age directly reduces friction and resistance to runoff can provide an estimate for the hydrological characteristics of the surfaces this can support applications such as rainfall runoff models risk assessment etc

26al 10be dating of an aeolian dust mantle soil in western new south wales australia abstract aeolian dust mantle soils are an important element of many landscapes in south eastern australia though the age of these aeolian deposits has not been radiometrically determined at fowlers gap in western new south wales surface cobbles of silcrete and quartz overlie a stone free aeolian dust mantle soil which has a thickness of about 1 6 m the clay rich aeolian dust deposit in turn lies upon a buried silcrete and quartz stone layer modelling in situ cosmogenic 26 al and 10 be concentrations measured in both the surface quartz stones and in the buried quartz layer of rocks reveals that each has experienced a complex exposure burial history due to the absence of quartz stones or sand at intermediate depths our cosmogenic 26 al and 10 be modelling was not able to determine a definitive mechanism of stone pavement formation and stone burial various scenarios of stone formation transport burial and exhumation were tested that constrain the age of the deposit to range from 0 9 0 2 ma to 1 8 0 2 ma based largely on different assumptions taken for the time dependency of the net sedimentation rate this corresponds with the initiation of the simpson desert dune fields and the deflation of lakes in central australia which probably responded to the shift to longer wavelength larger amplitude quaternary glacial cycles at around 1 ma sensitivity analyses were carried out to identify those parameters which better constrained model outputs within model errors which largely are the result of analytical errors in measured 26 al and 10 be concentrations all three competing theories of colluvial wash upward displacement of stones and cumulic pedogenesis are possible mechanisms for the formation of the surface stone pavement

intensified climate driven exhumation along the south himalayan front since one million years ago abstract this paper builds a database of apatite fission track aft ages and thermal modeling results covering the whole southern tibetan plateau providing detailed information on the cooling and erosion process of the modern landscape evolution and comparing with the distribution of climatic factors large scale aft age distribution and thermal history modeling results indicate extraordinarily intense erosion along the south himalayan front and relatively weak erosion in the interior of the plateau aft samples from different regions plot into different partitions on the elevation vs aft age diagram and there is an excellent coupling between aft ages and climatic factors based on aft thermal history modeling results an intensified erosion event since 1 myr ago has been identified along the south himalayan front the varied aft ages along the south himalayan front are probably induced by differential intensity of erosion in the same cooling event rather than the time when the rapid cooling event began meanwhile the spatiotemporal coupling of climatic factors and the intensified erosion belt suggests that climatic transition is the key factor dominating the rapid exhumation event since 1 myr

transition from arid to hyper arid environment in the southern levant deserts as recorded by early pleistocene cummulic aridisols abstract the time at which deserts established their current arid or hyper arid conditions remains a fundamental question regarding the history of earth cosmogenic isotope exposure ages of desert pavement and welded calcic gypsic salic reg soils that developed on relatively flat alluvial surfaces 2 ma ago in the negev desert indicate long geomorphic stability under extremely dry conditions over a short interval during their initial stage of development between 1 2 ma these cumulative soils are characterized by calcic soils reaching maximum stage iii of carbonate morphology this interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern negev desert since 1 ma pedogenesis changed toward more arid soil environment and the formation of gypsic salic soil horizons that were later followed by dust accumulation the dichotomy of only moderately developed calcic soil stages ii iii during a relatively long time interval 105 106 years indicates an arid environment that does not support continuous development but only occasional calcic soil formation the very low 18o and relatively high 13c values of these early pedogenic carbonates support soil formation under arid climatic conditions such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture this in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate at 1 ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern negev desert leading to deposition of soluble salts and dust deposited in the soils the combination of long term hyperaridity scarcity of vegetation and lack of bioturbation salts cementation dust accumulation and tight desert pavement cover has protected the surfaces from erosion forming one of the most remarkably stable landscapes on earth a landscape that essentially has not eroded but accumulated salt and dust for more than 106 yr

physical weathering in arid landscapes due to diurnal variation in the direction of solar heating despite the prominent role of physical weathering in arid and semi arid landscapes there has been little study of the specifi c processes responsible for the rapid breakdown of subaerially exposed rocks for example many boulders and cobbles in deserts exhibit fi ne near vertical cracks although workers have hypothesized that these and other cracks are initiated by diurnal heating and cooling no convincing specifi c mechanism for their formation has been proposed we have characterized these cracks at eight sites on surfaces of different ages in the mojave sonoran and chihuahuan deserts and the high desert of central new mexico our data reveal four basic types of cracks longitudinal surfaceparallel fabric related and meridional the orientations of the fi rst three types are associated with clast shape and rock fabric the azimuths of meridional cracks however are preferentially aligned north south typically with a nonrandom multimodal distribution we propose that these cracks are caused by tensile stresses that arise in the interior of clasts due to strong radial gradients in temperature that evolve and rotate in alignment with the sun s rays we suggest that the multimodal nature of crack orientations may be in part attributable to the seasonally varying latitude dependent solar elevation angle over millennial time scales we suggest that this thermal cracking is an effi cient weathering process that together with cumulic soil epipedon development creates the key attributes of most desert pavements in addition to individual clasts exposed on desert surfaces this mechanism of cracking is potentially signifi cant in other climates and on other planets as well as for rock outcrops and for man made structures

soil heterogeneity in mojave desert shrublands biotic and abiotic processes 1 geological and ecological processes play critical roles in the evolution of desert piedmonts feedback between fast cyclic biotic and slow cumulative pedogenic processes on arid alluvial fan systems results in a heterogeneous landscape of interspace and canopy microsites defining the spatial extent between these processes will allow a better connection to ecosystem service and climate change we use a soil chronosequence in the mojave desert and high spatial resolution infiltrometer measurements along transects radiating from canopies of perennial shrubs to assess the extent of biotic and abiotic processes and the heterogeneity of soil properties in arid shrublands results showed higher saturated conductivity under vegetation regardless of surface age but it was more conspicuous on older developed soils at proximal locations to the shrub bulk density soil structure grade silt and clay content significantly increased radially from the canopy while sand and organic material decreased soil properties at distal locations 2 5 times the canopy radius had no significant spatial correlation the extent of the biotic influence of the shrub was 1 34 0 32 times the canopy radius hydraulic properties were weakly correlated in space but 75 of the variance could be attributed to sand content soil structure grade mean particle diameter and soil organic material none of which are exclusively biotic or abiotic the fast cyclic biotic processes occurring under vegetation are clearly overprinted on slow cumulative abiotic processes resulting in the deterministic variability observed at the plant scale

effect of rock fragments on eolian deposition of atmospheric dust abstract the effect of rock fragments and rock fragment cover on the deposition of airborne dust was examined in a wind tunnel four parameters were studied pebble size pebble flattening cover density and wind speed the effect of these parameters on the deposition of dust on the pebbles on the deposition of dust bewween and underneath the pebbles and on total dust deposition pebbles interpebble space was measured separately deposition on the pebbles increased with pebble size pebble flattening and wind speed deposition between and underneath the pebbles increased with increasing wind speed and with decreasing pebble flattening but there was no consistent relationship with pebble size total dust deposition was not influenced by pebble size pebble flattening and cover density but it increased linearly with wind speed it was also demonstrated that the larger and the flatter the pebbles and the higher cover density the more the dust will tend to settle on the pebbles rather than between or underneath them air flow separation seems to play a primary role in the spatial distribution of dust deposition within a rock fragment field as it determines the location and size of the low sedimentation areas that are connected to the air flow separation bubbles it should be noted that all data in this study refer to dust deposition not accumulation since only wind velocities below the dust deflation threshold were used

cantor set model of eolian dust deposits on desert alluvial fan terraces available data show that eolian dust accumulation rates on desert alluvial fan terraces are often inversely proportional to the square root of the terrace age for a given area this temporal scaling is similar to that observed in fluvial and marine stratigraphic sequences in which a fractal distribution of hiatuses occurs i e a cantor set eolian dust accumulation on alluvial fan terraces is controlled by regional climatic influences on dust deposition e g dessication of pluvial lakes in the early holocene and local surface characteristics e g vegetation and pavement coverage that control dust preservation in order to interpret the observed scaling in terms of these relative influences i consider two end member models 1 a deterministic model in which dust deposition is controlled by cyclical climatic changes i e glacial interglacial cycles and in which no erosion occurs and 2 a stochastic model in which erosion and deposition take place with equal probability and magnitude during each time step i e a bounded random walk the observed temporal scaling is most consistent with the bounded random walk model suggesting that long term eolian dust accumulation is predominantly controlled by episodic changes in vegetation and pavement coverage over time and that eolian dust deposits are strongly punctuated by episodes of erosional reworking at a wide range of temporal scales

a note of caution on the use of boulders for exposure dating of depositional surfaces abstract exposure dating of boulders has been widely applied to determine the age of depositional surfaces under the assumption that the pre depositional nuclide component in most boulders is negligible here we present a case study on fluvial terraces at the active mountain front of the eastern andes where this assumption is clearly invalid because sandstone boulders n 13 from terraces at two sites contain a highly variable inherited 10be component and have apparent 10be ages that exceed the age of the respective surface by up to 90 ka likewise boulders from active stream channels n 5 contain a substantial inherited 10be component equivalent to 5 48 ka of exposure the age of the fluvial terraces is well determined by two approaches that allow to correct for the pre depositional nuclide component 10be dating of amalgamated pebbles and 10be depth profiles on sand samples at site 1 three terraces have 10be ages of 3 5 ka t2 11 13 ka t3 and 16 20 ka t4 which are consistent with the terrace stratigraphy the age of terrace t3 is confirmed by a calibrated 14 c age of 12 61 0 20 ka bp obtained from a wood sample at site 2 terrace t3 has a 10be age of 13 16 ka the average inherited 10be concentration of sand grains determined from depth profiles and stream sediments is small and equivalent to 1 3 ka of exposure in contrast the mean inheritance of pebbles and boulders is higher and equivalent to exposure times of 10 ka and 30 ka respectively these differences in the pre depositional nuclide component are related to the different provenance and transport history of sand pebbles and boulders the sand is derived from rapidly eroding miocene sediments exposed near the mountain front whereas the pebbles and boulders originate from triassic sandstones in the internal part of the fold and thrust belt on their way to the mountain front boulders and pebbles were temporarily stored and irradiated in alluvial fans that are currently reworked as sediment deposition in intramontane basins and their subsequent excavation is common in the andes and other fold and thrust belts the presence of pre depositional nuclide components should be evaluated when applying exposure dating at active mountain fronts

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

atmospheric dust in modern soil on aeolian sandstone colorado plateau usa variation with landscape position and contribution to potential plant nutrients rock derived nutrients in soils originate from both local bedrock and atmospheric dust including dust from fardistant sources distinction between fine particles derived from local bedrock and from dust provides better understanding of the landscape scale distribution and abundance of soil nutrients sandy surficial deposits over dominantly sandstone substrates covering vast upland areas of the central colorado plateau typically contain 5 40 silt plus clay depending on geomorphic setting and slope excluding drainages and depressions aeolian dust in these deposits is indicated by the presence of titanium bearing magnetite grains that are absent in the sedimentary rocks of the region thus contents of far traveled aeolian dust can be estimated from magnetic properties that primarily reflect magnetite content such as isothermal remanent magnetization irm isothermal remanent magnetization was measured on bulk sediment samples taken along two transects in surficial sediment down gentle slopes away from sandstone headwalls one transect was in undisturbed surficial sediment the other in a setting that was grazed by domestic livestock until 1974 calculation of far traveled dust contents of the surficial deposits is based on measurements of the magnetic properties of rock surficial deposits and modern dust using a binary mixing model at the undisturbed site irm based calculations show a systematic down slope increase in aeolian dust ranging from 2 to 18 of the surface soil mass similar to the down slope increase in total fines 18 39 of surface soil mass a combination of winnowing by wind during the past and down slope movement of sediment likely accounts for the modern distribution of aeolian dust and associated nutrients at the previously grazed site dust also increases down slope 5 11 in sediment with corresponding abundances of 13 25 fines estimates of the contributions of aeolian dust to the total soil nutrients range widely depending on assumptions about grain size partitioning of potential nutrients in weathered bedrock nevertheless aeolian dust is important for this setting contributing roughly 40 80 of the rock derived nutrient stocks p k na mn zn and

quaternary evolution of a hyperarid drainage under climatic fluctuations and rift margin base level fall ne negev israel abstract the long term bedrock incision of streams in the northeastern negev has been dictated since the early pliocene by the subsidence of the dead sea basin however this incision is accompanied by very long intervals of sediment aggradation here we document the quaternary scale fluvial response to changing base level lithology structure and climate along the hyperarid nahal zafit ne negev the oldest 1 2 ma alluvial remnants point to a widespread beveled bedrock pediment at the base of the hazera anticline this pediment like other stream pediment anticline relationships in the region provides the baseline framework into which nahal zafit incises during the early to middle pleistocene this pediment was the base level for all streams emerging out of the anticlines the tectonic subsidence of the regional base level at the rift margin farther downstream has caused incision and upstream migration of bedrock knickpoints triggering the development of a wide incised valley in the mazar syncline adjacent to the hazera anticline since 330 ka fluvial terraces landslides and taluses record intervals of basin wide fluvial deposition under prevailing hyperarid to arid climate despite the general arid climate prolonged fluvial deposition intervals occurred at ca 330 265 230 125 and 110 20 ka rapid and quite short duration bedrock incision occurred in between these much longer intervals of aggradation in addition to the proposed climatic imprint on fluvial aggradation incision cycles and the first order base level control of the rift margin fault the formation of strath terraces and distribution of stored sediments within the drainage basin point to the fundamental role that lithology and structure play in the quaternary evolution of the ne negev watersheds

measuring the time and scale dependency of subaerial rock weathering rates over geologic time scales with ground based lidar the evolution of roughness as a function of surface age was used to quantify weathering rates on rocky desert surfaces surface topography on eight late quaternary alluvial terraces which record the weathering of holocene 5 1 ka boulder strewn deposits into mature 87 2 ka desert pavements in the negev desert of israel was measured with ground based lidar roughness on each terrace was characterized with power spectral density psd analysis and changes in psd as a function of length scale 0 04 1 50 m and surface age were used to estimate diminution weathering rates of the surface rocks we found psd values that systematically increase as a power law function of roughness exponent of 2 0 and decrease as an inverse power law function of surface age this psd evolution indicates a fragmentation rock weathering process driven by salt shattering throughout the 87 k y period examined psd analysis of the lidar data also revealed weathering rates that increase with rock size and decrease as an inverse power law function of time from initial values 20 mm k y to 1 mm k y within 60 k y

the role of the nile in initiating a massive dust influx to the negev late in the middle pleistocene the late middle pleistocene initiation of loess accretion in the negev desert israel resulted from a chain of events starting with the exposure of shallow offshore nile delta sands beginning 180 ka during a period of glacially lowered eustatic sea level this exposure allowed the formation of the dunes of the sinai negev erg and the eastward movement of the dunes under the gusty glacial time winds in northern sinai this eastward dune advance occurred by eolian saltation that generated the coarse silts that accumulated downwind as loess we postulate that the absence of earlier negev loess is not a result of interglacial erosion as previously proposed but is due to the relatively recent convergence of the above conditions necessary for loess formation we based our interpretation on analyses of two long term natural dust traps and the association of coarse quartz silt production with the advancing quartz rich dunes over this carbonate terrain although the nile delta is considered an early to middle pleistocene feature and therefore could have been the source of sand throughout the quaternary it attained the shallow depth range of glacial interglacial sea level changes only during late marine oxygen isotope stage 7 to early stage 6 allowing its wide exposure in quaternary times prior to erg formation negev dust was finer composed of silt and clays derived from distal sources in the sahara and arabian deserts

reply to r leb hooke s discussion of use of multiparameter relative age methods for age estimation and correlation of alluvial fan surfaces on a desert piedmont eastern mojave desert california

the vesicular layer and carbonate collars of desert soils and pavements formation age and relation to climate change abstract the vesicular fine grained a horizon av is the widespread ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages now known to form mostly through accumulation of eolian dust recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation changes in the magnitude of eolian activity and effective leaching related to quaternary climatic changes are also hypothesized to have influenced the evolution of the av horizon numerical modeling geochronologic and field laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of av how the changing av horizon increasingly influences soil infiltration and carbonate translocation and accumulation and the control that clasts of the evolving pavement exert on pedogenic processes results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived eolian material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by av horizon formation the early development of a weakly to moderately developed av horizon directly over gravelly parent material in late and middle holocene soils moderately influences soil infiltration but significant leaching of very soluble materials and some carbonate in dust are permitted in older pleistocene soils however the texturally more mature av and underlying cumulic nongravelly horizons more strongly limit the rate and depth of leaching and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material other aspects of av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate referred to as carbonate collars development of a numerical model that integrates soil hydrology a co2 production diffusion model calcite kinetics and thermodynamic considerations composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation model results combined with results of 13c and 18o analyses of collar carbonate demonstrate how precipitation of calcite on pavement clasts and within the av is favored at a depth much shallower than that indicated by the classic carbonate depth climate relationship of jenny and leonard jenny h j leonard c d 1935 functional relationships between soil properties and rainfall soil science 38 363 381 and arkley arkley r j 1963 calculations of carbonate and water movement in soil from climatic data soil science 96 239 248 or simulated by numerical models of carbonate accumulation simultaneous development of thick carbonate collars and the av horizon requires the sustained pavement clast av horizon coupling for at least centuries to possibly millennia new thermoluminescence ages also indicate that much of the av horizon formed in the holocene and that it is certainly much younger than the older pleistocene pavements this supports the previously proposed hypothesis that increased dust flux during the pleistocene to holocene transition triggered and or greatly accelerated av horizon development an understanding of the genesis of collars provides not just an understanding of how carbonate can accumulate in surface environments but it also provides important clues into processes of pavement evolution and preservation of av horizons during long glacial periods the av horizon is not merely an insignificant surficial zone of recent dust accretion instead its development profoundly influences the genesis of desert soils and pavements

geomorphoclimatic characteristics and landform information in the ejina basin northwest china natural environment of mid latitude deserts of central asia is undergoing rapid changes one of its elements is the relief what needs to be particularly emphasized is its morphogenesis and landform evolution in this study a geomorphological research in the ejina basin inner mongolia is carried out with regard to identifying the main landforms and the contemporary geomorphic processes we consider ancient and modern landforms as a unit and provide a general explanation for their evolution related environmental indications of existing landforms are discussed on the basis of climate geomorphology results show that the current basin is under the conditions favorable for the development and dominance of landforms originated from physical processes such as desiccation deflation and aeolian the landform system is characterized by its variable structure which is conditioned by specific hydrodynamics processes that existed during glaciations it is suggested that landform patterns in ejina are under the strong influence of rapid and or intensive geomorphic processes these signatures reflect the regional dynamics of landform evolution as characterized by a very effective integration of tectonic and climate driven morphogenetic processes based on the present day climate data we infer an obvious linkage of desert gorges and pediments in the basin to ancient humid phases which provided high energy runoff for the formation of these landforms and were associated with erosional features under more humid and colder climate during the last glacial period desert plains and aeolian dunes in the central basin are the related products of contemporary climate clear evidences proving the landform inconsistency and landform instability in the ejina are presented indicating that the main geomorphic unit is experiencing transformation from alluvial plain to desert plain and then to aeolian dunes however the geomorphodiversity in the ejina should be a compound result of complex surficial processes other than glaciation frost weathering fluvial alluvial action desiccation deflation and aeolian processes as well as climatic changes have played important roles

geomorphology on geologic timescales evolution of the late cenozoic pacific paleosurface in northern chile and southern peru abstract the atacama desert on the western margin of the central andes is one of the driest and oldest deserts in the world it is defined by a distinct and ancient surface known as the pacific paleosurface pps or atacama paleosurface the age of this surface is determined as the time at which sediment deposition ceased and the surface was effectively abandoned early studies suggested that this abandonment took place between 14 and 10 ma and was related to both the uplift of the andes and the onset of hyperaridity in the region here we provide a regional re examination of the pps compiling existing work on the underlying geology sedimentology surface exposure dating and seismic profiling we also present new multispectral satellite maps of the pps and 45 new cosmogenic 3he and 21ne surface exposure ages in order to constrain the formation age and the preservation and incision history of the paleosurface we conclude that the pps is not a single paleosurface but instead is a mosaic of smaller surfaces that were formed by aggradational and degradational processes over 19 million years or more and should be termed collectively as the pacific paleosurfaces the time at which individual paleosurfaces formed is related to regional climate where the location of each is controlled by regional tectonic activity cosmogenic surface exposure ages suggest that the surfaces are a record of regional scale climate events

deposition of playa windblown dust over geologic time scales thick eolian deposits are commonly observed beneath desert pavements downwind of dust emitting playas these deposits play an important role in piedmont surface evolution controlling surface hydrologic conductivity and rates of pedogenesis to better understand the factors controlling the spatial distribution of eolian deposition we developed a numerical model that treats deposition from spatially distributed playa sources using analytic point source solutions for deposition from a gaussian plume the model also accounts for complex downwind topography as a test case model predictions were compared to eolian deposit thicknesses on eagle mountain piedmont southern amargosa valley california which receives dust from nearby franklin lake playa the close relationship between the model predictions and mapped thicknesses suggests that eolian transport and deposition can be modeled from basin to regional scales within this framework these results have important implications for hydrologic pedogenic and air quality problems

measurements of dust deposition in gansu province china 1986 2000 abstract dust samples collected monthly for 15 years from 50 urban sites in 10 cities in gansu province china provide information on modern rates of dust deposition in the desert and gobi areas and in the loess plateau dust deposition is highest during spring months and lowest during autumn months in both the desert and gobi areas and the loess plateau there is a significant positive correlation between dust deposition and dust event and an inverse correlation between dust deposition and precipitation the 15 year mean maximums in the desert and gobi areas and the loess plateau are 498 64 and 327 02 t km 2 year 1 respectively and the mean minimums are 290 22 and 180 86 t km 2 year 1 respectively drought may have a widespread major influence on the modern rates of the dust deposition

coastal aeolian dune development solheimasandur southern iceland abstract a coastal aeolian dune field on the distal parts of solheimasandur southern iceland is currently undergoing active construction ongoing sand deflation in the foreshore is demonstrated by the preservation of sand ridges in the downwind lee of obstacles while a backshore sandsheet is characterised by actively accumulating long wavelength wind ripples the main region of aeolian accumulation is in the immediate backshore where sand has accumulated to a thickness of up to 8 m and is largely stabilized by vegetation surrounding interdune areas have undergone repeated flooding by fluvial incursions from the adjacent jokulsa river and are characterised by mud drapes which lap against the lower flanks of neighbouring dunes widespread sand adhesion structures testify to the often damp nature of the substrate over 1200 vegetated and stabilized dunes nebkhas occupy a 5 km 2 area of wind deflated gravel sandur plain downwind from the main site of aeolian accumulation the nebkhas show strong relationships between plan form shape and height indicating that they have attained equilibrium morphology for the prevailing climatic conditions within the nebkha field dunes demonstrate a predictable downwind decrease in height spatial concentration and degree of sand stabilization a time series of aerial photographs documents the temporal evolution of the dune field and demonstrates that aeolian accumulation commenced about 1940 and has been ongoing to the present day prior to 1940 repeated outburst floods associated with catastrophic lake drainage events from the solheimajokull glacier 8 km inland were of sufficient magnitude to repeatedly destroy any incipient aeolian bedforms that developed although strong onshore winds and high rates of sediment supply promote aeolian sediment transport dune field development is rare in humid boreal and sub arctic climates as encountered in southern iceland because the availability of sediment for aeolian transport is usually severely limited by damp substrate conditions thus the airflow tends to be undersaturated with respect to its potential sand transporting capacity and dune construction can only occur because of the stabilizing influence of vegetation

on the formation of desert loess sequences of quartz rich coarse 20 63 m silt occur in many low and midlatitude unglaciated arid and semiarid areas and have been termed desert loess the processes by which these deposits are generated have been debated for decades all hypotheses to explain their origin seek to provide mechanisms for the generation of silt sized material without glacial grinding which is the main process involved in the production of coarse silt at high latitudes possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones mechanical weathering of silicate rocks and abrasion of sand grains in active dune environments during intense transport events examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt improvements in the characterization of desert loess particle size mineralogy and geochemistry are needed however to identify sources and sinks of coarse silt especially when combined with climatic back trajectory analysis properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations

soils of an eolian analog of the leasburg surface southern new mexico abstract in a dissected mostly sandy terrain along the rio grande valley border of southern new mexico a reddish brown coarse loamy haplargid in an eolian deposit has a stage ii carbonate horizon that is typical of soils of the leasburg surface 8000 15 000 yr b p the eolian deposit buries sediments and soils of late pleistocene age or older thus it does not fit in the chronological framework of the stepped sequence of geomorphic surfaces along the valley border in which age of the surfaces and their soils increases with increasing elevation of the steps because the eolian deposit occurs in isolated areas where its age relative to the stepped sequence cannot be demonstrated geomorphically soil characteristics are major tools for placing the deposit and its soil in the chronological scheme for the area on the basis of the stage ii carbonate horizon the eolian deposit is considered to be an eolian analog of leasburg alluvium one of the leasburg haplargids in eolian sediments on a ridge crest has a total of 23 kg m2 of pedogenic carbonate downslope in an area that receives runoff from higher areas a fine loamy haplargid in leasburg alluvium has 186 kg m2 of carbonate a nearby coarse loamy haplargid that does not receive runoff has only 46 kg m2 of carbonate thus landscape position and texture have a major influence on the total amount of pedogenic carbonate which can range to more than eightfold in soils of leasburg age

soil properties along a hillslope modified by wind erosion in the ordos plateau semi arid china abstract spatial variations of soil properties at three topographic sites along a hillslope were studied in the ordos plateau of semi arid china soil properties at the three positions of the hillside acted as disconnected values soil particles 0 5 mm in diameter decreased downslope and those between 0 05 and 0 5 mm formed a larger fraction of the soil in the midslope than in the summit or footslope total mass of c n and p in the middle slope soil was the lowest among the soils in the three topographic positions abnormality of carbonate content and of mineralogical components of the soil along the hillslope suggests wind transportation from outside sources this result indicates that the site had undergone several cycles of rapid erosion and deposition

clast size controls and longevity of pleistocene desert pavements at lathrop wells and red cone volcanoes southern nevada formation of desert pavement and accretionary soils are intimately linked in arid environments well sorted fallout scoria lapilli at lathrop wells 75 80 ka and red cone ca 1 ma volcanoes southern nevada formed an excellent parent material for pavement allowing infiltration of eolian silt and fine sand that first clogged the pore space of underlying tephra and then aggraded and developed vesicular a av horizons variations in original pyroclast sizes provide insight into minimum and maximum clast sizes that promote pavement and soil formation pavement becomes ineffective when clasts can saltate under the strongest winds while clasts larger than coarse lapilli are unable to form an interlocking pavement that promotes silt accumulation necessary for av development contrary to predictions that all pavements above altitudes of 400 m would have been reset in their development after late pleistocene vegetation advances the soils and pavements show clear differences in maturity between the two volcanoes this indicates that either the pavements and or soils develop slowly over many tens of thousands of years and then are very stable or if they are disrupted by vegetation advances subsequent pavements are re established with successively more mature characteristics

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

atmospheric mineral dust in dryland ecosystems applications of environmental magnetism irm mean of 67 samples 6 72 10 3 am 2 kg 1 is more than two orders of magnitude greater than that for underlying paleozoic and mesozoic sedimentary rocks this contrast is mainly caused by the presence of silt size titanium bearing magnetite particles in the surficial deposits and their absence in bedrock because of their size composition and isolated location the magnetite particles represent a component of atmospheric dust likely deposited over the past few centuries the positive correlation of sediment irm values with amounts of potential plant nutrients reveals the importance of atmospheric dust to soil fertility over much of the american southwest subsequent disturbance of landscapes by domestic livestock grazing as an example commonly results in wind erosion which then depletes exposed surfaces of original aeolian magnetite and associated fine grained sediment declines in soil fertility and water holding capacity in these settings can be estimated in some field settings via decreases in magnetic susceptibility relative to nearby undisturbed areas along gentle hillslope gradients of the colorado plateau field measures for aeolian magnetite demonstrate that the redistribution of deposited atmospheric dust influences landscape level patterns in the distribution of invasive exotic plant species our results indicate that environmental magnetism has high potential for assessing the development and degradation of dry landscapes elsewhere

beryllium 10 concentrations in the hyper arid soils in the atacama desert chile implications for arid soil formation rates and el nino driven changes in pliocene precipitation abstract meteoric 10be concentrations in soil were measured to understand the mechanism timescale and climatic dependence of soil formation in the hyper arid atacama desert the observed systematic decline of soil 10be concentrations with depth has been reproduced using a simple model that assumes soil matrix including 10be builds up as layers over time while 10be decays in situ this suggests a mechanism of soil accumulation via atmospheric deposition which is in agreement with stable isotopic evidence the model estimates an age of 6 6 0 4 ma for the total soil profile small discrepancies between the model and observations are likely mainly due to changes in precipitation rates that can impact 10be delivery rates and 10be movement within the profile interpreted in this way the 10be data suggest drying in the atacama after 4 7 ma and returning to an insignificant wet period at 1 ma which was possibly connected to el nino or la nina like climate change

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

pedogenesis on talus slopes the buckskin range nevada usa abstract soil development on steep mountainous topography generally leads to thin and undifferentiated pedons on talus slopes of the buckskin mountains a fault blocked range of west central nevada usa thick differentiated pedons occur talus occurs on the western front where block rotation has formed very steep slopes and consists of angular dacite cobbles and boulders the study area is arid averaging less than 20 cm of precipitation per year typical pedons consist of surface talus filled with vesicular non structured sandy loam to loam material this material overlies clay textured prismatic and blocky structured horizons mostly rock free that in places are over 1 m thick pedons are classified as fine mixed mesic xeralfic paleargids soil macro and micromorphological features soil mineralogy and soil chemical and physical attributes suggest the following developmental sequence which began sometime before the middle pleistocene the talus serves as a baffle to collect eolian dust once eolian dust accumulates to a threshold thickness primary minerals are transformed in situ mostly to a smectitic clay as clay content increases a second threshold level is reached at which time the horizon of clay enrichment has sufficient strength and shrink swell potential to support and raft the talus upward the exposed talus can then continue to trap eolian dust the soil profile thickens and the pedon is protected from erosion a variation of this soil cumulation process may be partially responsible for textural b horizon formation in avid and semiarid climates

a soil chronosequence on lake mega frome beach ridges and its implications for late quaternary pedogenesis and paleoenvironmental conditions in the drylands of southern australia abstract the terminal lake systems of central australia are key sites for the reconstruction of late quaternary paleoenvironments paleoshoreline deposits around these lakes reflect repeated lake filling episodes and such landforms have enabled the establishment of a luminescence based chronology for filling events in previous studies here we present a detailed documentation of the morphology and chemistry of soils developed in four well preserved beach ridges of late pleistocene and mid to late holocene age at lake callabonna to assess changes in dominant pedogenic processes all soil profiles contain evidence for the incorporation of eolian derived material likely via the formation of desert pavements and vesicular horizons and limited illuviation due to generally shallow wetting fronts even though soil properties in the four studied profiles also provide examples of parent material influence or site specific processes related to the geomorphic setting there is an overall trend of increasing enrichment of eolian derived material since at least 33 ka compared to the holocene profiles the derived average accumulation rates for the late pleistocene profiles are significantly lower and may suggest that soils record important regional changes in paleoenvironments and dust dynamics related to shifts in the southern hemisphere westerlies

fan and playa areas in southern california and adjacent parts of nevada in bolsons in the desert regions of southern california and adjacent parts of nevada the area underlain by alluvial fan gravels and playa sediments is generally 1 2 times the area being eroded to produce those sediments in certain larger basins in the vicinity of death valley however the depositional area is only about half the size of the erosional area this reflects the more active tectonic environment in these bolsons of the areas underlain by recent sediments in these bolsons playas make up 2 6 per cent smaller playas are found in the mojave region and seem to be associated with sedimentary terranes conversely igneous terranes support larger playas larger deviations of playa area from these averages are attributable to incorrect identification of bolson boundaries fine sediment is either able to pass through the bolson to the next down stream or is being collected from areas upstream that were not considered to be part of the system for example the playa in death valley is unusually large this is in part because the death valley playa has been deformed tectonically so parts of it are now eroding and in part because the outlet of lake tecopa was downcut in the geologically recent past so sediment once trapped there now reaches death valley the size of the playa in death valley is still adjusting to these changes

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

the history and nature of wind erosion in deserts recently the importance of wind erosion has been reevaluated many low angle surfaces developed on susceptible materials possess closed depressions pans and these often have a distinctive morphology and lunette dunes on their lee sides it has also become apparent that in drylands there are extensive areas of stone pavements some of which have been molded by deflation however it is now recognized that other horizontal sorting processes have played a role especially movement of fines by overland flow vertical sorting associated with wetting and drying salt heave bioturbation frost action and dust accretion have also played a role in hyperarid areas especially with unidirectional winds bedrock outcrops and old lake beds have been molded to give aerodynamic forms called yardangs the study of dust storms by analysis of climatological data and remote sensing has revealed the importance of deflation especially in hyperarid areas with centripetal drainage deflation hot spots such as the bo

influence of parent material and grain size on carbonate coatings in gravelly soils palo duro wash new mexico abstract close examination of carbonate coatings found on the bottoms of pebbles from gravelly soils indicates that soil hydraulic conductivity and respiration rate have a strong influence on the carbonate morphology of aridic soils clast size and lithology strongly correlate with coating thickness because of the nature of unsaturated flow within macropores of gravelly soils thicker coatings are found at the bottom of larger clasts coatings are thickest on limestone pebbles that commonly display dissolution features at their tops model values for soil co 2 based on gas diffusion predict soil atmospheric condition where soil water can remain undersaturated with respect to calcite and dissolve calcareous pebbles throughout the depth of the soil profile this coupled with soil hydrology creates a microenvironmental condition where the largest limestone clasts have the thickest coating a second phenomenon that is apparent from close observation of coatings is that soils containing abundant fines and translocated dust in the matrix have continuous coatings continuous coatings are absent however in soils that do not neighbor a dust source or do not have sufficient fines in the matrix in these soils coatings are almost completely absent from sand and granule size particles suggesting that zones of preferential flow in the soil inhibit carbonate precipitation in parts of the soil profile these inconstancies in the continuity and thickness of coatings suggest that stage iii morphology may not develop at the same rate even locally

erosion of ejecta at meteor crater arizona new methods for estimating erosion at meteor crater arizona indicate that continuous ejecta deposits beyond 1 4 1 2 crater radii from the rim 0 25r 0 5r have been lowered less than 1 m on the average this conclusion is based on the results of two approaches coarsening ofunweathered ejectainto surface lag deposits and calculation of the sediment budget within a drainage basin on the ejecta preserved ejecta morphologies beneath thin alluvium revealed by ground penetrating radar provide qualitative support for the derived estimates although slightly greater erosion 2 3 m of less resistant ejecta locally has occurred such deposits were limited in extent particularly beyond 0 25r 0 5r from the present rim subtle but preserved primary ejecta features e g distal ejecta lobes and blocks further support our estimate of minimal erosion of ejecta since the crater formed 50 000 years ago unconsolidated deposits formed during other sudden extreme events e g landslides exhibit similarly low erosion over the same time frame the common factor is the presence of large fragments or large fragments in a matrix of finer debris at meteor crater fluvial and eolian processes remove surrounding fines leaving behind a surface lag of coarse grained ejecta fragments that armor surfaces and slow vertical lowering

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

quantifying dust emissions from desert landforms eastern mojave desert usa abstract the measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models more than 500 individual dust measurements from eight common desert landforms in southern california were collected using the pi swerl portable in situ wind erosion lab the largest emitters of dust are dry washes 13 787 to 0 007 mg m 2 s 1 dunes playa margins distal alluvial fans and lacustrine beaches low emitters include salt crusted playas 0 692 to 0 002 mg m 2 s 1 silt clay crusted playas and desert pavements high emissions are a function of saltating sand that bombards the surface liberating dust sized particles for entrainment low dust emissions are primarily a function of surface crusting gravel armoring and vegetation density pi swerl measurements reveal that emission rates can vary by at least three orders of magnitude reflecting local variability in soil texture and continuity of surface crusts shear stress partitioning models can be applied to dust data measured by the pi swerl to account for large surface roughness features such as vegetation the results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the mojave desert and can potentially be used to improve atmospheric dust models

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

geochemical and magnetic characteristics of fine grained surface sediments in potential dust source areas implications for tracing the provenance of aeolian deposits and associated palaeoclimatic change in east asia abstract we investigated the geochemical and magnetic characteristics of fine grained surface sediments fractions

seismic quiescence before the 2000 m 7 3 tottori earthquake 1 we investigated the characteristics of the seismic quiescence associated with the 2000 m 7 3 tottori earthquake by applying the region time length rtl algorithm to the earthquake catalog of the japan meteorological agency jma we calculated the rtl parameters at the epicenter after eliminating aftershocks from the catalog and estimating its completeness the rtl parameters at the epicenter indicated that a seismic quiescencce started in 1999 and reached its minimum in may 2000 this quiescence is unlikely an artifact due to the changes of model parameters the close investigation indicated that the quiescence which appeared in a broad region around the epicenter during 1999 2000 is the only alarm group in study space and time and is therefore most probably a precursor of the tottori earthquake the seismicity changes revealed in this study may give better understanding of the seismo tectonics in the region and the preparation process of the tottori earthquake

field experiments of aeolian dust accumulation on rock fragment substrata the effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long term field experiment in the negev desert of israel four parameters were studied pebble eccentricity pebble size pebble flattening and cover density the effect of these parameters on the accumulation of dust on the pebbles on the accumulation of dust between and underneath the pebbles and on total dust accumulation pebbles interpebble space was measured separately accumulation on the pebbles increased as the pebbles became larger less flattened and more elongated and as cover density increased accumulation between and underneath the pebbles increased as the pebbles became smaller more flattened and more elongated and as cover density increased although the accumulation area available became smaller total dust accumulation increased as the pebbles became smaller more flattened and more elongated and as cover density increased rock fragments act as a dust trap as dust accumulation on pebble covered surfaces is several tens of times larger than dust accumulation on similar but pebble free surfaces however less than 20 of the initially settled dust is protected from further erosion in the negev desert dust erosion by wind is of the order of 10 times larger than dust erosion by water the rate of long term dust accumulation in the negev is of the order of 15 30 g m 2 yr 1 this is considerably lower than the rates proposed elsewhere in the literature which are based upon over optimistic dust retainment percentages

dry aeolian dust accumulation in rocky deserts a medium term field experiment based on short term wind tunnel simulations the spatial pattern of medium term a few months dry aeolian dust accumulation in rocky deserts is predicted using short term deposition and erosion experiments in a wind tunnel the predictions are tested in a field experiment set up in the northern negev desert of israel the results show that superimposing wind tunnel deposition and erosion maps usually leads to correct predictions of medium term dust accumulation the predictions are somewhat less confident near the inflection lines of windward hillslopes where small scale irregularities in the local topography make it difficult to locate the exact position of the areas of little accumulation elsewhere in the topography predictions are good and the method works satisfactorily highest accumulation occurs on concave windward slopes and to a lesser extent on slopes parallel to the wind little accumulation occurs on the convex windward slopes and in dust separation bubbles the smallest accumulation rates are observed immediately upwind of the top of pronounced hills and on leeslopes the rate of dry dust accumulation measured during the field experiment varied from 17 to 93 g m 2 a 1 depending on the topographic position of the accumulation plots for most plots it was of the order of 30 60 g m 2 a 1

rocky 7 prototype mars rover field geology experiments 1 lavic lake and sunshine volcanic field california experiments with the rocky 7 rover were performed in the mojave desert to better understand how to conduct rover based long distance kilometers geological traverses on mars the rover was equipped with stereo imaging systems for remote sensing science and hazard avoidance and 57fe mossbauer and nuclear magnetic resonance spectrometers for in situ determination of mineralogy of unprepared rock and soil surfaces laboratory data were also obtained using the spectrometers and an x ray diffraction xrd xrf instrument for unprepared samples collected from the rover sites simulated orbital and descent image data assembled for the test sites were found to be critical for assessing the geologic setting formulating hypotheses to be tested with rover observations planning traverses locating the rover and providing a regional context for interpretation of rover based observations analyses of remote sensing and in situ observations acquired by the rover confirmed inferences made from orbital and simulated descent images that the sunshine volcanic field is composed of basalt flows rover data confirmed the idea that lavic lake is a recharge playa and that an alluvial fan composed of sediments with felsic compositions has prograded onto the playa rover based discoveries include the inference that the basalt flows are mantled with aeolian sediment and covered with a dense pavement of varnished basalt cobbles results demonstrate that the combination of rover remote sensing and in situ analytical observations will significantly increase our understanding of mars and provide key connecting links between orbital and descent data and analyses of returned samples

zeolites in soil environments the limited occurrence of these minerals has resulted in a scant knowledge about their properties in the soils zelazny and calhoun 1977 as pointed out by the above authors the occurrence of natural zeolites in soils is rare and not well known and only about 75 papers have been published describing the occurrence of zeolites in soils these occurrences range from hot humid soils in india to cold arid soils in the dry valleys of antarctica most of these reports describe residual zeolite phases that have persisted from the parent material during soil formation however there are reports of zeolites that have formed in soil environments a variety of natural zeolites have been found in soils including analcime chabazite clinoptilolite gismondine laumontite mordenite natrolite phillipsite and stilbite over the past 25 years natural zeolites have been examined for a variety of agricultural and environmental applications because of their unique cation exchange adsorption and molecular sieving properties and their abundance in near surface sedimentary deposits natural zeolites have been used as soil conditioners slow release fertilizers carriers for insecticides and herbicides remediation agents in contaminated soils and dietary supple ments in animal nutrition ming and allen this volume pond 1995 these applications can result in direct or indirect incorporation of natural zeolites into soils if these minerals are to be used effectively in these applications it will be necessary to understand the long term stability and effects of zeolites in soils or soil like systems several reviews have been published on the occurrences and properties of zeolites in soils zelazny and calhoun 1977 ming and dixon 1987c ming and dixon 1988 ming and mumpton 1989 boettinger and graham 1995 this chapter provides an overview and update on the occurrence of zeolites in soils and briefly describes methodology used for identifying and characterizing zeolites

the origin and distribution of salts on alluvial fans in the atacama desert northern chile the atacama desert has been predominantly hyperarid since the middle miocene combined ionic and x ray diffraction analysis shows that calcium sulphate is prevalent on three similar alluvial fans in salar basins across a transect of different environments in antofagasta province northern chile differences between the fans were largely due to the effect of local factors on salt input secondary redistribution and deposit preservation thus carbonate was notable in the high andes fan c and pre cordillera fan b whereas in the central valley fan a greater qualities of the more soluble salts chlorides and nitrates probably reflect the higher level of aridity and an oceanic source the camanchaca calcium sulphate distribution on the alluvial fans and on adjacent hilltops indicates an aeolian origin evidence from the pre cordillera fan b however suggests that salt input may have been episodic related to changes in conditions within the general aridity and possibly to stone pavement and soil development calcium sulphate sources range from an input in andean precipitation and the camanchaca to abundant regional evaporite deposits it is probable however that products of andean volcanism constitute the dominant primary source of calcium sulphate and that the salt has subsequently been distributed widely within the endoreic basins of the region by a combination of groundwater surface flow and the wind 1997 john wiley sons ltd

ground penetrating radar as a tool for probing the shallow subsurface of mars 1 design and testing of an impulse ground penetrating radar gpr for possible rover deployment on mars in 2009 is well underway the gpr has mass power volume and data rate targets of 0 5 kg 3 w peak 3400 cm3 and 0 3 mb d and will possess easily modified bistatic high frequency e g 500 600 mhz and monostatic rat tail e g 100 mhz antennas the gpr should be capable of measuring in situ radar properties on mars to depths of up to 10 20 m thereby helping to constrain near surface geology and structure initial gpr tests at the site of the 2001 fido rover field trials near cronese lake california confirm the value of the instrument in defining local geologic setting and in providing context for data collected using other rover science payload elements a rover deployed gpr may enable three dimensional mapping of local stratigraphy which in turn can assist in evaluating the history of aqueous activity and the accessibility of near surface water