soil seal development under simulated rainfall structural physical and hydrological dynamics this study delivers new insights into rainfall induced seal formation through a novel approach in the use of x ray computed tomography ct up to now seal and crust thickness have been directly quantified mainly through visual examination of sealed crusted surfaces and there has been no quantitative method to estimate this important property x ray ct images were quantitatively analysed to derive formal measures of seal and crust thickness a factorial experiment was established in the laboratory using open topped microcosms packed with soil the factors investigated were soil type three soils silty clay loam zcl sandy silt loam szl sandy loam sl and rainfall duration 2 14 minutes surface seal formation was induced by applying artificial rainfall events characterised by variable duration but constant kinetic energy intensity and raindrop size distribution soil porosities derived from ct scans were used to quantify the thickness of the rainfall induced surface seals and reveal temporal seal micro morphological variations with increasing rainfall duration in addition the water repellency and infiltration dynamics of the developing seals were investigated by measuring water drop penetration time wdpt and unsaturated hydraulic conductivity kun the range of seal thicknesses detected varied from 0 6 5 4 mm soil textural characteristics and om content played a central role in the development of rainfall induced seals with coarser soil particles and lower om content resulting in thicker seals two different trends in soil porosity vs depth were identified i for sl soil porosity was lowest at the immediate soil surface it then increased constantly with depth till the median porosity of undisturbed soil was equalled ii for zcl and sl the highest reduction in porosity as compared to the median porosity of undisturbed soil was observed in a well defined zone of maximum porosity reduction c 0 24 0 48 mm below the soil surface this contrasting behaviour was related to different dynamics and processes of seal formation which depended on the soil properties the impact of rainfall induced surface sealing on the hydrological behaviour of soil as represented by wdtp and kun was rapid and substantial an average 60 reduction in kun occurred for all soils between 2 and 9 minutes rainfall and water repellent surfaces were identified for szl and zcl this highlights that the condition of the immediate surface of agricultural soils involving rainfall induced structural seals has a strong impact in the overall ability of soil to function as water reservoir

slip rate measurements on the karakorum fault may imply secular variations in fault motion beryllium 10 surface exposure dating of offset moraines on one branch of the karakorum fault west of the gar basin yields a long term 140 to 20 thousand year right lateral slip rate of 10 7 0 7 millimeters per year this rate is 10 times larger than that inferred from recent insar analyses 1 3 millimeters per year that span 8 years and sample all branches of the fault the difference in slip rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales such fluctuations would be consistent with mechanical coupling between the seismogenic brittle creep and ductile shear sections of faults that reach deep into the crust

discovery of the palaeo indus delta fan complex the indus river carries sediments from the western himalaya and deposits some of these as channel and floodplain sediments or molasse the rest of its load forms the indus delta at the margin of the indian ocean the indus delta passes some of its sediments to be deposited as indus submarine fan turbidites thus as elsewhere himalayan molasse delta and fan deposition are related hi tune and space however when we examine fluvial and marine age range data of the older indus deposits in terms of this sedimentary assemblage a major portion of its marine record is missing the oldest known molasse along the indus suture zone and hi the foredeep are middle eocene and late palaeocene hi age respectively a recent synthesis of sedimentation in the northern indian ocean however shows that turbidite sedimentation started around early miocene in the modern indus fan and even later in the bengal fan where are the palaeogene indus delta and fan sediments we suggest herein that these are preserved as the palaeogene siliciclastic khojak formation hi the katawaz basin and eastern makran the modern indus river is 2900 km long coumes kolla 1984 and has 30 000 m 3 s 1 discharge milliman et al 1984 in summer fig 1 twice that of the mississippi river the annual suspended sediment load wells coleman 1984 varies between 395 and 435 x 10 3 t almost equal to that of the mississippi the existence of the middle eocene to middle miocene indus molasse along the

radon 222 in groundwater of the long valley caldera california in the long valley caldera where seismicity has continued essentially uninterrupted since mid 1980 and uplift is documented samples of water from hot warm and cold springs have been collected since september 1982 and their222rn concentrations analyzed concurrently rocks encompassing the hydrologic systems feeding the springs were analyzed for their radioelement contents because their uranium is the ultimate source of the222rn in the water

late quaternary glacier advances in the upper catchment area of the indus river ladakh and western tibet abstract geomorphological mapping in the markha valley and the northern nimaling mountains northern zanskar range has revealed eight prominent glacial stages the two oldest glaciations are marked by glacial abrasion forms as ice scour limits and glacial benches above the lower and middle markha valley these glaciations probably occurred prior to the last glacial cycle furthermore terminal and lateral moraines glacial tongue basins basal moraines and tills provide evidence for three glacial stages in the markha and nimaling valleys when the equilibrium line altitude ela depression was 670 350 m the glaciations probably occurred during the lgm the lateglacial and the lower holocene as indicated by the topographic sequence the ela depressions and the tentative glacial stratigraphic divisions for the north indian areas large moraine complexes in the vicinity of the present glaciers probably represent three glacial stages of neoglacial and historical glacial advances the ela depressions are 10 70 m the present glaciation of the nimaling mountains largely restricted to north flanks and the glacier basins below covers an area of 45 55 km2 the modern ela is calculated at 5650 5750 m a s l on north faces rising to about 5900 6000 m a s l on south faces in the central and southern parts of the ayila ridge western tibet present elas range from 5700 to 5800 m a s l on the north facing slopes to 6000 6100 m a s l on southern slopes eight former glacier stages are preserved on the southwest flank of these mountains by lateral and terminal moraine ramparts the ela depressions amount to 640 950 m

event frequency and landscape stability on the floodplain systems of arid central australia abstract central australian floodplains contain landforms suggesting activity at three scales a set of large sand sheets sand threads and megaripple covered channels related to a few enormous floods the contemporary floodplain which consists of channels and levees floodouts unchannelled floodplains and floodbasins and erosion cell mosaics which result from local redistribution of sediment classical floodplain models do not fit these systems which behave more like low angle alluvial fans because they continue to accumulate sediment the sedimentary history of the central australian floodplains suggests that deposition in the last 10 000 years has been dominated by a few gigantic floods these events are not represented in the published slackwater deposit record but morphological evidence for them can be found in bedrock gorges as well as on floodplains since the last major flood channel levee systems have been growing slowly upwards and outwards and outwards from the mountain ranges away from these systems sediment supply is limited and the dominant process is local reworking this has intensified since the arrival of europeans 100 years ago and also as a result of increased flooding due to variations in rainfall

transport of radon in flowing boreholes at stripa sweden granitic rock in an underground experimental waste storage site at stripa sweden is unusually high in natural radioelements 40 ppm uranium with higher concentrations occurring locally in thin chloritic zones and fractures consequently groundwater seeping through fractures into open boreholes is highly anomalous in its radon content with activity as high as 1 ci 1 when total count gamma ray logs are run in boreholes where groundwater inflow is appreciable the result is quite unusual the radon daughter activity in the water adds considerably to the gamma contribution from the rock and in fact often dominates the log the total gamma activity increases where radon charged groundwater enters a borehole and decays as the water flows along the hole in response to the hydraulic gradient as a consequence the gamma log serves as a flow profile locating zones of water entry or loss by an increase or decrease in the total gamma activity if mixing within the borehole does not occur the activity decreases exponentially along the hole away from the entry point because of the steady decay of radon and its daughter products as they migrate with the flow in the water column this spatial decay rate can be converted to a linear flow rate since the 3 8 day half life of radon governs the response time for example if the volumetric flow rate in a 76 mm hole falls within the range 0 5 50 liters per day and if observations are available from a 10 m length of hole then the flow rate can be measured quantitatively proportionately higher rates can be measured if longer hole lengths are available for observation a model for flow through a thin crack emanating radon at a rate e shows that the radon concentration of water entering a hole is e h where is the radon decay rate and h the crack aperture assuming that the flow rate and crack source area are such that an element of water resides within the source area for several radon half lives or more using this simple relationship independent measurements of emanation and concentration produce reasonable estimates of fracture aperture although uranium concentration values at stripa are unusually high neither the emanation coefficients nor the fracture properties appear to be unusual for granitic rock it therefore seems likely that many granitic sites must exist where the radon content in groundwater is higher than in other geological terranes although perhaps not as high as the microcurie per liter concentrations found at the stripa site

earthquake induced soft sediment deformation in the lower shyok river valley northern ladakh india abstract soft sediment deformation structures occur in the 150 m thick pliocene quaternary fluvio lacustrine sediments exposed around the khalsar and tirit areas in the lower shyok river valley northern ladakh and eastern karakoram india these structures vary in morphology and pattern and occur at different stratigraphic horizons they satisfy the criteria for attributing them to seismic events and it is proposed that these structures were formed as a result of earthquake induced liquefaction the deformation structures are thus interpreted to represent pre historic seismic events which occurred up to 5 ma ago and were associated with tectonic activity along the karakoram fault

controls on the spatial and temporal variability of 222rn in riparian groundwater in a lowland chalk catchment radon is a powerful tracer of stream aquifer interactions however it is important to consider the source and behaviour of radon in groundwater when interpreting observations of river radon in relation to groundwater discharge here we characterise the variability in groundwater radon concentrations in the riparian zone of a chalk catchment groundwater 222rn radon concentrations were determined in riparian zone boreholes at two sites in the lambourn catchment berkshire uk over a two year period in addition borehole core material was analysed for 226ra radium and to determine radon emanation radon and radium concentrations and radon emanation were found to change with depth and temporal variations in groundwater radon concentrations were found at different scales the abundance of radium and emanation of radon increased nearer the surface leading to greater groundwater radon concentrations it is shown that seasonal changes in water table elevation can to lead to variable radon concentrations in groundwater as zones of radon production become hydraulically active groundwater radon concentrations in shallow piezometers were found to respond to both seasonal changes in the water table and individual rainfall events riparian sources of radon can be variable and are therefore potentially influential in the radon signals observed in rivers and should be properly characterised when interpreting river radon inputs

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

introducing a terrestrial carbon pool in warm desert bedrock mountains southwestern usa growth of the phoenix metropolitan area led to road cut or house platform exposures of the internal bedrock material of surrounding semiarid mountain ranges similar exposures in the surrounding sonoran and mojave deserts reveal the presence of sedimentary calcium carbonate infilling the preexisting fracture matrix of the bedrock field surveys at 31 sites with bedrock fractures filled with carbonate referred to as bffc in the following text reveal an average of 0 079 0 036 mtc m2 stored in the upper 2 m of analyzed bedrock exposures backscattered electron microscopy images indicate the presence of carbonate at the micron scale not included in this estimate of carbon storage pilot radiocarbon and sr isotope analyses suggest that one of the surveyed bffc veins was flushed into the bedrock from a nonbedrock source during the wetter last glacial period in the late pleistocene

fractal analysis of drainage basins on mars 1 we used statistical properties of drainage networks on mars as a measure of martian landscape morphology and an indicator of landscape evolution processes we utilize the mars orbiter laser altimeter mola data to construct digital elevation maps dems of several mostly ancient martian terrains drainage basins and channel networks are computationally extracted from dems and their structures are analyzed and compared to drainage networks extracted from terrestrial and lunar dems we show that martian networks are self affine statistical fractals with planar properties similar to terrestrial networks but vertical properties similar to lunar networks the uniformity of martian drainage density is between those for terrestrial and lunar landscapes our results are consistent with the roughening of ancient martian terrains by combination of rainfall fed erosion and impacts although roughening by other fluvial processes cannot be excluded the notion of sustained rainfall in recent mars history is inconsistent with our findings

sand detachment by wind driven raindrops wind movement and velocity can have a profound effect on some aspects of the soil erosion process in the case of wind driven rain differences in raindrop trajectory are expected wind driven raindrops achieve some degree of horizontal velocity which increases their resultant impact velocity and they strike the soil surface at an angle deviated from the vertical under the effects of both gravitational and drag forces however not much is known about the physical impact of raindrops on a soil in situations where this impact is at an angle and it is also not precise known if oblique raindrops have stronger erosive effects than vertical ones a series of tests was conducted to assess the effect of wind velocities on sand detachment from splash cups in a wind tunnel facility equipped with a rainfall simulator splash cups packed with standard sand were exposed to windless rains and to rains driven by horizontal wind velocities of 6 10 and 14 m s 1 to evaluate the sand detachment by wind driven raindrops the average angle of rain inclination from vertical was calculated from the direct intensity measurements implemented with windward and leeward facing raingauges placed at different slopes a kinetic energy sensor measured energy of windless and wind driven rains results showed that the kinetic energy flux calculated by the resultant impact velocity of drops adequately described the sand detachment from the splash cups by wind driven raindrops however an additional analysis of pearson correlation coefficients using the velocity components rather than the resultant velocity of wind driven raindrops indicated that the energy flux related to the horizontal component of wind driven raindrops had a greater correlation with sand detachment than that related to the normal component this finding contradicted the general assumption that the component of velocity normal to the surface is related to the detachment copyright 2005 john wiley sons ltd

a field investigation into the effects of progressive rainfall induced soil seal and crust development on runoff and erosion rates the impact of surface cover abstract surface crusts and seals can form from a variety of processes both physical and biological and have the potential to alter runoff and erosion especially in regions with low vegetation covers despite the obvious links between seals and crusts these features have rarely been considered together this study uses rainfall simulation experiments to investigate interrill soil crust and seal development in response to structural or raindrop impact induced and depositional or runoff induced processes on a semiarid piedmont in southern new mexico usa which has undergone substantive vegetation change replacement of grasses by shrubs over the last 100 years the study design incorporates six double paired runoff plots divided into four subplots each of which was exposed to three rainfall simulation events crust development on these plots was assessed using penetration resistance measurements while seal development was assessed using runoff coefficients the penetration resistance data indicate that subplots directly exposed to raindrop impacts uncovered plots have crusts that are 40 stronger than those positioned beneath a mesh cover covered plots that intercepts the kinetic energy of the rainfall the crusts exposed to raindrop impacts increased in strength following each simulation whereas the crusts on the covered surfaces reached a plateau after two events runoff data indicate that seal development does not directly mirror crust formation runoff coefficients increased after each rainfall simulation event but were not significantly different between the covered and uncovered plots rather the presence of stone lags or litter on the soil surface influenced the relation between runoff and seal development sediment yields from uncovered surfaces exceeded those from covered surfaces indicating that raindrop impacts contribute to the delivery of sediment into flows the results of this study indicate that the loss of vegetation cover on the piedmont has increased the extent of surface crust and seal development but that those crusts may be playing an important role in mitigating erosion

size characteristics of sediment in interrill overland flow on a semiarid hillslope southern arizona this study examines the size characteristics of sediment removed from a semiarid hillslope by interrill overland flow rainfall simulation experiments were conducted on a runoff plot 18 m wide and 35 m long established on a piedmont hillslope in southern arizona the top of the plot coincided with the hillslope divide and its outlet was located within a shallow rill samples of runoff were obtained from two cross sections located in the interrill portion of the plot upslope of the rill and from a calibrated flume through which was directed interrill overland flow reaching the bottom of the plot analyses of sediment contained in these samples showed that sediment in interrill flow is finer than the matrix soil the fineness of the interrill sediment compared to the matrix soil appears to be due to the inability of interrill overland flow to transport the coarser fraction of the sediment supplied to it by raindrop detachment this finding implies that the rate of soil erosion in interrill areas is not as is commonly supposed limited by the rate at which raindrops can detach sediment but by the rate at which they detach sediment of a size that the overland flow is competent to transport the relative fineness of sediment eroded from this hillslope is consistent with other evidence for the recent evolution of shrub covered hillslopes in southern arizona

reconstruction of a major storm event from its geomorphic signature the ladakh floods 6 august 2010 extreme precipitation events in arid mountain regions determine flood debris flow and landslide hazards and are principal drivers of geomorphic change increased frequency of intense precipitation in many regions of the world over the past few decades increases the importance of documenting and understanding such events when they occur we use the geomorphic record to reconstruct the distribution and magnitude of river discharge from a devastating convective storm event in the interior of the western himalaya we use this record to estimate the rates magnitudes and distribution of precipitation and magnitude of debris flows generated by the same event the storm occurred on 6 august 2010 over the ladakh range in the northwest indian himalaya killing 600 people and devastating more than 60 villages it triggered numerous debris flows and significantly widened the lower reaches of the main tributary valleys we demonstrate that rainfall was concentrated in a 6 km wide range parallel band centered 4 5 km up from the range front and that within this band precipitation intensity was 30 times that above it at least 75 mm of rain fell in 30 min during the heaviest part of the storm which is at least 1 5 times the highest 24 h maximum for the previous 100 yr the results demonstrate that the geomorphic record can be used to constrain the intensity of rainfall without meteorological stations and also record its distribution better than could be achieved with normal densities of instrumentation

the implications of laboratory222rn flux measurements to the radioactivity in groundwaters the case of a karstic limestone aquifer laboratory time scale experiments were conducted on carboniferous limestone gravels from the mendip hills area england with the purpose of evaluating the release of 222 rn to the water phase the specific surface areas of the samples were 4 14 and 1 69 cm 2 g 1 which provided respectively values of 50 6 and 12 7 pci for the released rn these results allowed the calculation of the emanation coefficient of this rock matrix with respect to the release of rn where completely different values corresponding to 23 and 6 were found suggesting that the extent to which grain boundaries or imperfections in aggregates of micro crystals of calcite intersect the particle surface certainly affects the rn release they also permitted the evaluation of models for the generation of rn in rocks and transfer to water in order to interpret the radioactivity due to this gas in groundwaters from the karstic aquifer of the mendip hills area where the calculated activities in groundwater based on the values of 23 and 6 for the emanation coefficient were about 51 and 15 times higher than actually measured in groundwater therefore the emanation coefficient in nature is considerably smaller than in the lab experiment and another factor k 0 k 1 may be introduced into the equations related to the modelling with the aim of adjusting the theoretical practical results

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

above the weathering front contrasting approaches to the study and classification of weathered mantle abstract weathered mantle comprises the materials above bedrock and below the soil it can vary in thickness from millimeters to hundreds of meters depending primarily on climate and parent material study of the weathered mantle comes within the realms of four disciplines geology geomorphology soil science and civil engineering each of which uses a different approach to describe and classify the material the approaches of engineers geomorphologists and geologists are contrasted and compared using example papers from the published literature soil scientists rarely study the weathering profile as such and instead concentrate upon soil forming processes and spatial distribution primarily in the solum engineers including engineering geologists study the stability and durability of the weathered mantle and the strength of the materials using sophisticated procedures to classify weathered materials but their approach tends to be one dimensional furthermore they believe that the study of mineralogy and chemistry is not useful geomorphologists deal with weathering in terms of process how the weathered mantle is formed and with respect to landform evolution using a spatial approach geologists tend to ignore the weathered mantle because it is not bedrock or to study its mineralogy and or chemistry in the laboratory i recommend that the approaches of the various disciplines be integrated geomorphologists and geologists should consider using engineering weathering classifications and geologists should adopt a spatial perspective to weathering as should engineers and engineering geologists

gps measurements from the ladakh himalaya india preliminary tests of plate like or continuous deformation in tibet observations of relative motion in a geodetic network in ladakh india and across southern tibet indicate slow shear on the karakorum fault rapid east west extension across the whole of southern tibet and constant arc normal convergence between india and southern tibet along the himalayan arc measurements of ten campaign style and six permanent sites with global positioning system gps precise geodesy provide these bounds on the style and rates of the large scale deformation in the tibet himalaya region divergence between sites at leh ladakh india and shiquanhe western tibet as well as slow relative motion among sites within the ladakh network limit right lateral slip parallel to the karakorum fault to only 3 4 5 mm yr this low rate concurs with a recent estimate of 3 4 mm yr for late holocene time but disagrees with the much higher rate of 30 35 mm yr that has been used to argue for plate like behavior of the tibetan plateau convergence between ladakh and the indian subcontinent at 18 8 3 mm yr at 224 17 1 differs little from estimates of convergence across the central segment of the himalaya finally lengthening of the baseline between leh ladakh and lhasa in southeastern tibet at 17 8 1 mm yr or between leh and bayi farther to the southeast at 18 3 mm yr is consistent with an extrapolation of rates of east west extension of the tibetan plateau based both on shorter gps baselines e g lhasa simikot and on diverging slip vectors of earthquakes in the himalaya we interpret these results to indicate that tibet behaves more like a fl uid than like a plate

a meta analysis of soil erosion rates across the world abstract over the last century extraordinary efforts have been devoted to determining soil erosion rates in units of mass per area and time under a large range of climatic conditions and land uses and involving various measurement methods we undertook a meta analysis of published data from more than 4000 sites worldwide the results show that there is extraordinarily high variability in erosion rates with almost any rate apparently possible irrespective of slope climate scale land use land cover and other environmental characteristics however detailed analysis revealed a number of general features including positive relationships of erosion rate with slope and annual precipitation and a significant effect of land use with agricultural lands yielding the highest erosion rates and forest and shrublands yielding the lowest despite these general trends there is much variability that is not explained by this combination of factors but is related at least partially to the experimental conditions our analysis revealed a negative relationship between erosion rate and the size of the study area involved significant differences associated with differing measurement methods with direct sediment measurement yielding the lowest erosion rates and bathymetric radioisotope and modeling methods yielding the highest rates and a very important effect of the duration of the experiment our results highlight that when interpreting erosion rates the experimental conditions involved must be taken into account even so the data suggest that only order of magnitude approximations of erosion rates are possible and these retain a very large degree of uncertainty consequently for practical purposes such as calculation of global sediment budgets empirical equations are not a substitute for direct measurements our results also show that a large proportion of the experiments have been short term less than 3 years which reduces dramatically the reliability of the estimated erosion rates given the highly non normal behavior of soil erosion time dependency despite the efforts already made more long term measurement experiments need to be performed especially in regions of the world that are under represented in global datasets in addition protocols need to be established for standardizing the measurement methods and reporting the results to enable data to be compared among diverse sites

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

recoil emanation theory applied to radon release from mineral grains abstract in this paper the recoil emanation theory is presented as a major mechanism for rn release from solid materials the basic theory is developed for rn emanation from geometrical shapes spheres and cylinders having variable thickness of precursor ra containing material subsequently a sphere pore model of emanation from mineral grains like those in rocks soils etc is developed in this model a surface of the grain is constructed as a superposition of in and out directed spherical caps and cylindrical pores the model incorporates processes like rn embedding pore overlap water effect and emanation from the edges using such a geometrical model it is shown how the rn emanating power measurements can give a clue to the ra distribution and surface properties of the samples in particular it is shown that for grains reasonably larger than the recoil range and for surface ra distribution the emanating power is independent of the grain size but the total ra concentration varies with the reciprocal of the grain size the opposite is true for ra distributed uniformly throughout the volume of the grain it is shown how the rn emanating power is related to the surface porosity of the grain also implications are made with respect to u transport in nature and with respect to low emanating power from lunar soil finally a failure of the emanation theory is discussed to reproduce emanation curves for the samples having high specific surface areas and ra distributed throughout the volume

late quaternary fluvial activity in the dry valleys mekgacha of the middle and southern kalahari southern africa kalahari dry fossil valleys mekgacha have been little used in palaeoenvironmental reconstruction partly because the origins and functions of the valleys are a subject of debate and partly because they contain few datable sediments in the middle kalahari the valleys are endoreic and following a decline in ground water tables owing to human interference over the past 150 years rarely contain water evidence from three sites suggests that the valleys contained standing water between 15000 and 12000 yr bp and that the main okwa mmone system flowed into palaeolake makgadikgadi at 920 m a s l during this period the southern kalahari contains the exoreic molopo network which is hydrologically more active being prone to surface flows in response to extreme rainfall events the spring fed kuruman valley has two terraces the lower composed of a series of flood deposits of late holocene age the flood of february 1988 provides a useful analogue for the conditions under which these deposits were formed and of the temporal regime of the kuruman river comparison with adjacent sites suggests that evidence put forward to indicate cycles of climatic amelioration in the last 4000 yr may in part represents the effect of extreme precipitation events historical floods show a strong correlation to southern oscillation high phase cold event episodes suggesting possibilities for extension of the southern oscillation record through palaeoflood studies

sand transport under increased lateral jetting of raindrops induced by wind abstract wind tunnel experiments for raindrop detachment and wind driven transport rd wdt process were conducted under improved lateral jetting induced by wind velocities of 6 4 10 and 12 m s 1 at nozzle operating pressures of 75 100 and 150 kpa wind driven rainfalls were also incident on the windward and leeward slopes of 4 and 9 to have a broad variation in the angle of incidence the objective of this experimental set up was to distinguish the roles of both impact components of obliquely striking wind driven raindrops on rd and wind on wdt raindrop impact components and reference horizontal wind were quantified by normal etz and horizontal etx kinetic energy fluxes and wind shear velocity u respectively to physically model the process of rd wdt the results showed at each level of u differential sand transport rates by rd wdt qm rd wdt occurred depending on the magnitude of raindrop impact components and qm rd wdt increased as the relative contribution of etz increased although etx was more correlated with qm rd wdt than etz the extreme increases in etx at the expense of etz brought about no increases but decreases in qm rd wdt an rd wdt model was built under the process of examining the discrete effects of etz and etx on rd together with u and resulted in a better coefficient of determination r2 0 89 than only total kinetic energy et did alone with u r2 0 84 in this study etx was strongly related to u and not to etz which was the principal difference from the previous rainsplash studies which relied on the compensatory lateral jet development by the compressive pressure build up at the raindrop soil interface including etx in the rd wdt model both separated the distinct role of each raindrop impact component in rd and improved the performance of u in wdt by better distinguishing its interaction with etx which was not explicitly separated in previous models of rd wdt

limit of strain partitioning in the himalaya marked by large earthquakes in western nepal great earthquakes in the himalaya are thought to occur mostly along the range front field mapping and radiocarbon dating reveal earthquake rupture on a previously unrecognized fault in the interior of the western himalaya which forms part of a key structural component of the mountain range implying that seismic risk evaluations should be revised

water repellency and pore clogging at early successional stages of microbiotic crusts on inland dunes brandenburg ne germany abstract biological soil crusts play a key role for hydrological processes in many open landscapes they seal the topsoil and generate surface run off utilization of the mineral substrate at early stages of microbiotic crusts was investigated using scanning electron microscopy sem water repellency indices were measured using the ethanol water microinfiltrometer method and steady state water flow was determined on the dry crusts and after 300 600 1200 and 1800 s of wetting thus allowing to follow pore clogging through swelling of extracellular polymeric substances eps it was found that water repellency increases with initial crust development where filamentous cyanobacteria and filamentous green algae were dominating but decreases as coccal algae bryophytes and fungi associated with bryophytes emerged swelling of eps took place immediately after wetting and its influence on steady state water flow was most pronounced when filamentous cyanobacteria and algae partially filled in the matrix pores and enmeshed sand grains still leaving micropore channels available for free water infiltration but prior to appearance of coccal algae bryophytes and associated fungi which formed a dense cover on the surface it was concluded that a new phase of crust succession was accompanied by easier wettability but slower infiltration transition from hydrophobicity to pore clogging as ruling mechanisms causing water run off may occur during wetting of individual biological crusts but also during crust succession over time

the u isotopes modeling in aquifers from pocos de caldas plateau brazil u modeled groundwater residence times were estimated by changes in 234u 238u activity ratio ar and u content of groundwaters from pocos de caldas city situated at the pocos de caldas alkaline massif brazil the estimated ages are more realistic than others generated by the use of hydraulic conductivity data and available information about the weathering rate of rocks in the plateau the 234u 238u ar and reciprocal of the dissolved u content data also defined a ternary plot that allowed the calculation of the relative volume of three source waters for the mixed water such u isotopes modeling for mixing calculations indicated that the dominant phase 68 in the mixture is thermal

identification of debris flow hazards in warm deserts through analyzing past occurrences case study in south mountain sonoran desert usa abstract after recognition that debris flows co occur with human activities the next step in a hazards analysis involves estimating debris flow probability prior research published in this journal in 2010 used varnish microlamination vml dating to determine a minimum occurrence of 5 flows per century over the last 8100 years in a small mountain range of south mountain adjacent to neighborhoods of phoenix arizona this analysis led to the conclusion that debris flows originating in small mountain ranges in arid regions like the sonoran desert could pose a hazard two major precipitation events in the summer of 2014 generated 35 debris flows in the same study area of south mountain providing support for the importance of probability analysis as a key step in a hazards analysis in warm desert settings two distinct mechanisms generated the 2014 debris flows intense precipitation on steep slopes in the first storm and a firehose effect whereby runoff from the second storm was funneled rapidly by cleaned out debris flow chutes to remobilize pleistocene debris flow deposits when compared to a global database on debris flows the 2014 storms were among the most intense to generate desert debris flows indicating that storms of lesser intensity are capable of generating debris flows in warm desert settings the 87 sr 86 sr analyses of fines and clasts in south mountain debris flows of different ages reveal that desert dust supplies the fines thus wetter climatic periods of intense rock decay are not needed to resupply desert slopes with fines instead a combination of dust deposition supplying fines and dirt cracking generating coarse clasts can re arm chutes in a warm desert setting with abundant dust

controls on flash flood magnitude and hydrograph shape upper blue hills badlands utah although many arid badland channels erode rapidly channel flows appear to be rare raising the issue of the character and frequency of flows responsible for channel erosion using an acoustic stream gauge we recorded nine flash flood hydrographs over a 3 yr period from the upper blue hills badlands utah with maximum discharges up to 9 m3 s flow hydrographs reveal bores and rapid depth changes that are similar to flash floods observed elsewhere bore and hydrograph peak translation velocities are greatest in narrow channel segments rapid runoff generation during short duration thunderstorms produced complex hydrographs whose shapes appear to reflect channel network geometry storm runoff response is highly sensitive to antecedent moisture which greatly reduces the regolith infiltration capacity high antecedent moisture coupled with a relatively low intensity long duration rainstorm produced the largest flow event estimating flow frequency in this landscape therefore requires knowledge of the distributions of both storm sizes and temporal spacing relative to the short time required for the regolith infiltration capacity to recover following wetting here roughly 24 hr landscape changes can be produced not only by rare large rainfall events but by a broad range of storm size and frequency under optimal antecedent moisture conditions

splash saltation trajectories of soil particles under wind driven rain abstract it is usually recognized that relatively large amounts of soil particles cannot be transported by raindrop splashes under windless rain however the splash saltation process can cause net transportation in the prevailing wind direction since variations in splash saltation trajectory due to the wind are expected in wind driven rain therefore determining the combined effect of rain and wind on the process should enable improvement of the estimation of erosion for any given prediction technique this paper presents experimental data on the effects of slope aspect slope gradient and horizontal wind velocity on the splash saltation trajectories of soil particles under wind driven rain in a wind tunnel facility equipped with a rainfall simulator the rains driven by horizontal wind velocities of 6 10 and 14 m s 1 were allowed to impact three agricultural soils packed into 20 55 cm soil pans placed at both windward and leeward slopes of 7 15 and 20 splash saltation trajectories were measured by trapping the splashed particles at distances downwind on a 7 m uniform slope segment in the upslope and downslope directions respectively for windward and leeward slopes exponential decay curves were fitted for the mass distribution of splash saltation sediment as a function of travel distance and the average splash saltation trajectory was derived from the average value of the fitted functions the results demonstrated that the average trajectory of a raindrop induced and wind driven soil particle was substantially affected by the wind shear velocity and it had the greatest correlation r 0 96 for all data with the shear velocity however neither slope aspect nor slope gradient significantly predicted the splash saltation trajectory more significantly a statistical analysis conducted with nonlinear regression model of c1 u 2 g showed that average trajectory of splash saltation was approximately three times greater than that of typical saltating sand grain

detachment and transportation of loose sediments by raindrop splash summary laboratory experiments on sediments ejected by splash consisted of two parts quantities ejected and mean projected distances were measured since the splash tray was 100 cm long and 20 cm wide and since both measurements were made on a receiving screen of one square metre it was obvious that only part of the translocated sediment was caught it was subject to serious doubt that the measured distances were representative for all sediment translocated if it is stated that the ejected sediment is distributed according to an exponential function around any point of impact located on the tray and if by definition tray and rainfall are perfectly homogeneous the ratio of the true to the measured distance and the ratio of the caught to the translocated sediment are only a function of the exponent of the real function the apparent distance being also a function of this exponent is thus the only factor needed to solve the two questions hence all empirical data were transformed into true data

effects of microbiotic crusts under cropland in temperate environments on soil erodibility during concentrated flow several studies illustrate the wind and water erosion reducing potential of semi permanent microbiotic soil crusts in arid and semi arid desert environments in contrast little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter this study attempts to fill the research gap through a a field survey assessing the occurrence of biological soil crusts on loess derived soils in central belgium in space and time and b laboratory flume 2 m long experiments simulating concentrated runoff on undisturbed topsoil samples 0 4 0 1 m2 quantifying the microbiotic crust effect on soil erosion rates three stages of microbiotic crust development on cropland soils are distinguished 1 development of a non biological surface seal by raindrop impact 2 colonization of the soil by algae and gradual development of a continuous algal mat and 3 establishment of a well developed microbiotic crust with moss plants as the dominant life form as the silt loam soils in the study area seal quickly after tillage microbiotic soil crusts are more or less present during a large part of the year under maize sugar beet and wheat representing the main cropland area on average the early successional algae dominated crusts of stage 2 reduce soil detachment rates by 37 whereas the well developed moss mat of stage 3 causes an average reduction of 79 relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover b 0 024 for moss dominated and b 0 006 for algae dominated crusts in addition to ground surface cover by vegetation and crop residues microbiotic crust occurrence can therefore not be neglected when modelling small scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments copyright 2007 john wiley sons ltd

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

comparative study of 222rn 40ar 39ar and 37ar leakage from rocks and minerals implications for the role of nanopores in gas transport through natural silicates we have measured the leakage of radiogenic 222rn and 40ar and reactor produced 39ar and 37ar in samples of granites plagioclase orthoclase cleavelandite and hornblende to assess the role of nanopores in gas transport through them the 39ar and 37ar were produced by fast neutron irradiation of the samples in vacuum sealed ampoules the leakage of all three ar isotopes was barely measurable in contrast the leakage of 222rn ranged between 1 45 18 1 orders of magnitude higher than that of the ar isotopes the extremely low ar isotope leakage suggests that the samples studied are not permeated by extensive nanopore networks which intersect grain surfaces the relatively high 222rn loss from these samples therefore has to be attributed to preferential enrichment of 226ra 238u on grain surfaces or to the existence of u th accessory minerals in or around grain boundaries from which substantial quantities of 222rn escape

quaternary fluvio lacustrine deposits of the lamayuru basin ladakh himalaya preliminary multidisciplinary investigations preliminary multidisciplinary investigations were carried out in a 105 m thick late pleistocene terrestrial sequence in the lamayuru basin ladakh himalaya palaeomagnetic studies reveal a reversal of polarity at about 35 ka bp this is the only report of this reversal event in the late pleistocene terrestrial sequences of the indian subcontinent the valley fill sequence is the product of an interplay of lacustrine with fluvio deltaic to colluvial processes four fossiliferous horizons have yielded ostracods and gastropods indicating shallow freshwater conditions the lamayuru lake was created by tectonically induced instabil ity about 35 40 ka bp an event that may be represented widely throughout the himalaya

bulk density of surface crusts depth functions and relationships to texture abstract a range of soils from pleistocene deposits with sandy to sandy loam textures and a group of loess derived soils with predominantly silty textures were subjected to 60 mm of simulated rainfall to form structural seals after drying samples of the surface crusts were collected to determine their bulk densities at a high resolution of depth 0 15 mm using an immersion method the bulk density data obtained for each soil sample were plotted as a function of depth beneath the soil surface two models were fitted to these plots the first was an exponential decay type function as proposed by mualem et al 1990 and the second was a sigmoidal type of function assuming that maximum compaction had already progressed to some depth below the soil crust surface all of the results indicated a gradual decrease in the bulk density with depth below the surface until convergence with the initial bulk density of the undisturbed soil was attained the maximum bulk densities recorded for crust segments representing the uppermost 2 mm of the crusts ranged from 1 713 to 1 91 g cm 3 for soils with silty sand loamy sand or sandy loam textures crusts of loess derived soils showed lower values ranging from 1 44 to 1 65 g cm 3 the maximum surface bulk density was shown to be highly significantly correlated with the log of geometric mean diameter of the primary grain size distribution in most cases both models showed good to very good fits to the measured data the exponential decay function appeared to better represent the initial stages of surface compaction and the sigmoidal function the later stages of structural crust formation

assessment of physical and hydrological properties of biological soil crusts using x ray microtomography and modeling biological soil crusts bscs are formed by aggregates of soil particles and communities of microbial organisms and are common in all drylands the role of bscs on infiltration remains uncertain due to the lack of data on their role in affecting soil physical properties such as porosity and structure quantitative assessment of these properties is primarily hindered by the fragile nature of the crusts here we show how the use of a combination of non destructive imaging x ray microtomography xmt and lattice boltzmann method lbm enables quantification of key soil physical parameters and the modeling of water flow through bscs samples from kalahari sands botswana we quantify porosity and flow changes as a result of mechanical disturbance of such a fragile cyanobacteria dominated crust results show significant variations in porosity between different types of crusts and how they affect the flow and that disturbance of a cyanobacteria dominated crust results in the breakdown of larger pore spaces and reduces flow rates through the surface layer we conclude that the xmt lbm approach is well suited for study of fragile surface crust samples where physical and hydraulic properties cannot be easily quantified using conventional methods

sand detachment under rains with varying angle of incidence abstract in the case of wind driven rain as the angle of rain incidence increases greater force components act parallel to the surface and lower force components act perpendicular to the surface therefore raindrop impact angle could influence the detachment process in the existence of substantial lateral jet development this could be particularly significant for a cohesionless sand surface that has a weaker resistance to the dislodgement by a raindrop impact than a soil surface experiments of simulated wind driven rain were conducted to evaluate sand detachment rates under increased lateral jetting induced by wind velocities of 6 4 10 0 and 12 0 m s 1 at nozzle operating pressures of 75 100 and 150 kpa and incident on windward and leeward slopes of 4 and 9 with these set ups it was possible to have varying angles of incidence and to determine the effect of the compressive stress and shear stress evaluated by the horizontal and vertical kinetic energy fluxes e tx and e tz respectively on the detachment rates from the sand surface at the same vectorwise sum of e tz and e tx the results showed that there was for similar values of e tz and e tx in windward slopes more sand detachment rate however for dissimilar values of e tz and e tx in leeward slopes where e tx was significantly higher than e tz there was less sand detachment rate consequently with certain values of the compressive stress and shear stress the sand detachment rates under wind driven rains peaked and e tz was the limiting component since the rates significantly decreased as e tz particularly decreased in spite of very large values of e tx

impact of consecutive extreme rainstorm events on particle transport case study in a sonoran desert range western usa abstract quantifying erosion rates in different landscape settings provides insight into how landforms change under different climatic tectonic and anthropogenic influences sediment traps designed to capture grus detached from granitic hill crests of an arid sonoran desert mountain range were placed prior to every precipitation event over a three year period just above rills that drain areas between 18 and 68 m 2 the slopes are underlain by moderately to strongly weathered granitic rocks to a depth of about a meter within this 3 year window a 1000 year precipitation event followed 27 days later by a 500 year event detached granitic grus in amounts far greater than previous storms capturing between 22 and 63 the average amount transported in the previous 59 rain events indicating the non linear nature of the response of grus detachment to precipitation intensity considering every precipitation event over a 3 year period no detachment occurred from events with less than 2 mm of total rainfall and only minimal erosion occurred from rainfall events with totals between 2 and 10 mm with durations typically less than 30 min detachment increased greatly with rain intensities of 36 mm h or more grus detachment from these arid crests increases with drainage area a higher percentage of exposed soil and steeper slopes 87 sr 86 sr ratios reveal that suspended sediment transported from hill crest to trap derives from recycled dust and not the local granite bedrock

fracture characteristics in weathered granites abstract the variability of weathered materials is an important factor in the geotechnical characterization of rock for engineering purposes most engineering rock mass classifications include weathering schemes that separate the weathering profile into zones or grades that depend upon the engineering and geological properties of the rock many geotechnical characteristics including weathering are controlled by the density and arrangement of fractures within the rock but the relationships between fracture patterns and weathering grades are typically not addressed fracture characteristics were investigated in 13 exposures in five study areas in weathered granite in eastern asia all weathering grades were present but never in the same exposure two approaches were used to evaluate the field data 1 joint spacings were tabulated and examined within each weathering grade tabulated classification and 2 each exposure was classified according to the dominant weathering grade visual classification mean and median joint spacings and joint spacing frequency distributions were analyzed and compared statistically for each approach the box fractal dimensions for joint spacing were calculated for exposures classified visually in each weathering grade three dimensional models of fresh and weathered granite were also generated and sampled for comparison to the field data mean joint spacing is usually 25 or more closer in weathered granite than it is in fresh granite and the difference between the mean spacings for weathered granite and fresh granite tend to be statistically significant there are no significant differences between any distribution medians the joint spacing distributions for weathered granite and fresh granite are also not statistically significantly different and there are no significant differences among the joint spacing frequency distributions for the different grades of weathered granite fractal analysis of joint spacings however suggests spacing characteristics of fresh and slightly weathered sw granite are very different from those in moderately highly and completely weathered granite and sampling of three dimensional models for weathered and fresh granite supports this in an engineering context this suggests that joint spacing relationships in the various grades of weathered granite can be treated as the same regardless of weathering grade and that joint patterns in fresh granite must be evaluated separately this knowledge could result in significant time and cost savings in the geotechnical characterization of these materials

estimating the effect of tree uprooting on variation of soil horizon depth by confronting pedogenetic simulations to measurements in a belgian loess area 1 spatial patterns of soil often do not reflect those of topographic controls we attempted to identify possible causes of this by comparing observed and simulated soil horizon depths observed depths of e bt bc c1 and c2 horizons in loess derived soils in belgium showed a weak to absent relation to terrain attributes in a sloping area we applied the soil genesis model soilgen2 16 onto 108 1 1 m2 locations in a 1329 ha area to find possible causes two scenarios were simulated model 1 simulated soil development under undisturbed conditions taking slope aspect and loess thickness as the only sources of variations model 2 additionally included a stochastic submodel to generate tree uprooting events based on the exposure of trees to the wind outputs of both models were converted to depths of transitions between horizons using an algorithm calibrated to horizon depths observed in the field model 1 showed strong correlations between terrain attributes and depths for all horizons although surprisingly regression kriging was not able to model all variations model 2 showed a weak to absent correlation for the upper horizons but still a strong correlation for the deeper horizons bc c1 and c2 for the upper horizons the spatial variation strongly resembled that of the measurements this is a strong indication that bioturbation in the course of soil formation due to treefalls influences spatial patterns of horizon depths

impact of wind on the spatial distribution of rain over micro scale topography numerical modelling and experimental verification the wind driven rain effect refers to the redistribution of rainfall over micro scale topography due to the existence of local perturbed wind flow patterns rainfall measurements reported in the literature point to the fact that the wind driven rain distribution can show large variations over micro scale topography these variations should be taken into account in hillslope hydrology in runoff and erosion studies and in the design of rainfall monitoring networks in practice measurements are often not suitable for determining the wind driven rain distribution therefore a few researchers have employed numerical modelling in order to provide confidence in using numerical models experimental verification for a range of different topographic features is imperative the objective of this study is to investigate the adequacy of a two dimensional computational fluid dynamics cfd model to predict the wind driven rain distribution over small scale topography the numerical model is applied to a number of topographic features including a succession of cliffs a small isolated hill a small valley and a field with ridges and furrows the numerical results are compared with the corresponding measurement results reported in the literature it is shown that two dimensional numerical modelling can provide a good indication of the wind driven rain distribution over each type of micro scale topography that is considered in this study it is concluded that more detailed verification procedures are currently inhibited due to the lack of available and detailed spatial and temporal rainfall data from field measurements copyright 2005 john wiley sons ltd

soft sediment deformation structures in the late quaternary sediments of ladakh evidence for multiple phases of seismic tremors in the north western himalayan region abstract the exposed quaternary sections of ladakh show evidence of seismicity during the late quaternary multiple levels of soft sediment deformation structures seismites are recorded from the quaternary sediments of the spituk leh along indus suture zone isz and the khalsar palaeolakes along shyok suture zone ssz and karakoraum fault kf the studied sections are a part of two major tectonically formed palaeolakes at 35 000 yr bp nine levels of seismites from spituk leh and eight levels from khalsar sections are recorded the deformed sediments comprise of clay silts and sand and are restricted to a single stratigraphic layers bounded by undeformed beds suggesting synsedimentary deformation the various deformational structures identified are simple and complex convolutes pinch and swell bedding microfolds and microfaults flame like structures pseudonodules clay diapirs ball and pillow structures pillar structures sedimentary dykes and mud lenses the release of stress along the isz ssz and kf may have been responsible for inducing seismicity in the area during the late quaternary times which may have caused liquefaction as a direct consequence of permanent deformation of ground surface due to earthquakes of large magnitudes 5 intensity the chronological data suggests release of stresses along isz ssz and kf in the form of earthquakes between 35 000 yr bp to approximately the last glacial maxima lgm as evident form the available chronology

radioelements radiogenic helium and age relationships for groundwaters from the granites at stripa sweden abstract the solution of radioelements and radiogenic 4he by groundwaters in fractured rocks is dependent upon the radioelement distribution in the rock matrix and the extent of the rock water interface the 234 u 238 u activity ratio and the dissolved u rn and he contents of such groundwaters respond to changes in the flow regime with time although 234 u 238 u activity ratios change with groundwater residence time as a consequence of 234th recoil induced solution of 234u the activity ratio is strongly influenced by the u distribution within fractures by the extent of the rock water interface and by the amount of 238u in solution a model for the quantitative evaluation of these effects is presented groundwaters from depths up to 880 m in the stripa granite have variable dissolved uranium contents and 234 u 238 u activity ratios the uranium geochemistry is primarily determined by variations in flow path rather than by groundwater age dissolved radiogenic 4he in the groundwaters increases with their depth of origin and is dependent upon the u content of the granite and upon its fracture porosity it increases with groundwater residence time but movement of 4he by diffusion and transport processes make the actual groundwater age indeterminate

land use effects on soil crusting and hydraulic response of surface crusts on a tropical alfisol soil surface crusting a common phenomenon on cultivated soils has major implications for agriculture and the environment because of its effects on soil hydrological properties erosion and crop establishment the objectives of this study were to evaluate land use controls on crust formation and the hydraulic response of soils to crust development for a patancheru series soil clayey skeletal mixed isohyperthermic udic rhodustalf in south central india soil aggregates obtained from cultivated pl and naturally vegetated fallow nv land were packed into sample trays and subjected to laboratory rain simulation to form crusts thin sections and visual observation indicated that crust development reached a more advanced stage in the pl case compared with nv following 90 min of rain at 40 80 mm h 1 intensity this was reflected in a thicker crust layer with fewer voids in the former and a less smooth surface with partially disintegrated aggregates in the latter the hydraulic response of the soil surface with the progression of crust development indicated a more permeable and less dense crust formed on nv than on pl soil the results suggested that nv soil aggregates were more stable and that crust formation is more gradual for stable aggregates compared with the less stable pl aggregates a structural crust type formed on the patancheru soil by means of parallel subprocesses involving translocation and illuviation of aggregate disruption by products and raindrop compaction and particle rearrangement copyright 1999 john wiley sons ltd

average sand particle trajectory examined by the raindrop detachment and wind driven transport rd wdt process recent studies of soil loss by the integrated action of raindrop impact and wind transport have demonstrated the significance of this mechanism this paper presents data obtained during wind tunnel experiments examining the raindrop detachment and wind driven transport rd wdt process to investigate average sand particle trajectory and the spatial extent at which the process operates in the experimental design at the same time as the horizontal wind velocities of 6 4 10 and 12 m s 1 passed through the tunnel rainfall was simulated falling on very well sorted dune sand the aspect and slope of the sand bed was varied to reproduce both windward ww and leeward lw slopes of 4o and 9o with respect to the prevailing wind direction the average sand particle trajectories by the rd wdt process were estimated by a mass distribution function which was integrated over a 7 m uniform slope segment the results showed that depended statistically upon the wind shear velocity u and the effect of the slope gradient was insignificant on this was different from that of the windless rain process raindrop detachment and splash driven transport rd st the spatial range of which relies strongly on additionally was approximately 2 27 2 2 times greater than the average path of a typical saltating sand particle of the rainless wind wind erosion saltation transport we st copyright 2009 john wiley sons ltd

sedimentation pattern in a trans himalayan quaternary lake at lamayuru ladakh india abstract located on the indo tsangpo suture zone lamayuru lake in western ladakh was created by neotectonic instability around 35 40 ka the valley fill sequence about 110 m thick reveals an interplay of lacustrine to fluvio deltaic to colluvial processes operating in response to changing climate and tectonic conditions based on integrated approach of sedimentology and palaeontological analysis we propose a sedimentation model for lamayuru lake with reference to changing climatic conditions and neotectonics the coarsening upward succession was divided into five lithofacies associations associations a e each association comprising one or more lithofacies represents a specific depositional environment and marks an independent episode of sedimentation a dominantly muddy sequence of facies association a a product of a lacustrine environment is followed by coarsening upward cycles association b composed of silt to sand that implies laterally shifting deltas thereafter thick sand and gravel deposits constituting fining upward fu unit cycles associations c and d represent deposition in a fluvial domain the upper part of association d composed of matrix supported gravel horizons was deposited as debris flows and marks the termination of sedimentation in the valley the clastic lithofacies facies associations a to d with plant fragments and charcoal presumably indicate warm humid climatic conditions in contrast association e comprising marl lithofacies occurring at four different levels is biogenic and indicates arid to semi arid climatic phases five main types of trace fossils including rhizoliths seem to be representatives of scoyenia ichnofacies and animal burrows indicating a thin population of soft bodied annelid and arthropod communities living under low energy condition nine fossiliferous horizons have yielded characteristic ostracods charophytes and gastropods indicating shallow low energy and cold water ecological conditions coarsening up lake succession extensive synsedimentary deformation tilting of lake beds and the entrenchment of the lamayuru drainage indicate basin evolution under an effective role of neotectonics in the area

crater formation in soils by raindrop impact the process of crater formation by the impact of water drops on soil sand and various other target material was studied craters of various shapes and sizes were observed on different target materials or conditions ranging from circumferential depression to completely hemispherical shape crater shape was dependent upon target material its ow stress or shear strength and the presence and thickness of water on the surface between 5 and 22 per cent of impact energy was spent on cratering but the relationship between crater volume and kinetic energy of a raindrop was curvilinear indicating a lower ef ciency of impact energy in removing target material as the energy increases impact impulse on the other hand showed a more linear relationship with crater volume and the ratio of impulse over crater volume i v remained constant for the entire range of drop sizes impact velocities and surface conditions used in this study surface shear strength represented by the penetration depth of fall cone penetrometer appeared to be a key factor involved in this process an equation was developed which related crater volume to cone penetration depth and impact impulse crater volume which appeared to be a better indicator of the total amount of material dislodged by a raindrop than splash amount can thus be predicted using this equation copyright 2004 john wiley sons ltd

geohydrologic geochemical and geologic controls on the occurrence of radon in ground water near conifer colorado usa abstract integrated studies of geohydrology geochemistry and geology of crystalline rocks in the vicinity of conifer colorado reveal that radon concentrations do not correlate with variations in concentrations of other dissolved species concentrations of major ions show systematic variations along selected groundwater flowpaths whereas radon concentrations are dependent on local geochemical and geologic phenomena such as localized uranium concentration in the rock or the presence of faults or folds when radon enters the flow system concentrations do not increase along flowpaths because its decay rate is fast relative to groundwater flow rates radon 222 is not in secular equilibrium with 238u and 226ra in the water therefore most of the 238u and 226ra necessary to support the waterborne 222rn must be present locally in the rock high concentrations of dissolved radon are not found in zones of high transmissivity and transmissivity is not correlated with rock type in the study area a higher transmissivity can be indicative of higher water volume to rock surface area ratios which could effectively dilute 222rn entering the water and or may indicate that emanated radon is carried away more rapidly water samples collected from individual wells over periods of several months showed significant fluctuations in the dissolved 222rn content this fluctuation may be controlled by changes in the contributions of water producing zones within the well resulting from seasonal fluctuations of the water table and or pumping stresses

differential responses of hillslope and channel elements to rainfall events in a semi arid area the degree of hydrological connectivity of hillslope elements in a semi arid climate was studied at the season and event timescales field data were obtained in rambla honda a medalus project field site situated in se spain on micaschist bedrock and with 300 mm annual rainfall the season timescale was assessed using correlation analysis between soil moisture and topographic indices the event timescale was studied by a quasi continuous monitoring of rainfall soil moisture runoff and piezometric levels results show that widespread transfers of water along the hillslope are unusual because potential conditions for producing overland flow or throughflow are spatially discontinuous and extremely short lived during extreme events runoff coefficients may be locally high ca 40 on slope lengths of 10 m but decrease dramatically at the hillslope scale 10 on slope lengths of 50 m two mechanisms of overland flow generation have been identified infiltration excess and local subsurface saturation from upper layers the former occurs during the initial stages of the event while the latter which is quantitatively more important takes place later and requires a certain time structure of rainfall intensities that allow saturation of the topsoil and the subsequent production of runoff hillslopes and alluvial fans function as runoff sources and sinks respectively permanent aquifers are lacking in rambla honda variable proportions of hillslope areas may contribute to flash floods in the main channel but their contribution to the formation of saturated layers within the sediment fill is very limited

digital processing of back scatter electron imagery a microscopic approach to quantifying chemical weathering this paper introduces digital processing of back scattered electron bse imagery as a microscopic approach to measure porosity from in situ dissolution of minerals four case studies exemplify this technique cases 1 and 2 explore the initiation and maintenance of weathering forms in case 1 alveoli start in the sedona area of arizona when sandstone porosity exceeds 32 this threshold is probably the point at which intergrain cohesion is reduced enough for shear stresses to erode grains case 2 examines the maintenance of gnamma pits and polygonal cracks on a basalt boulder on the island of maui hawaii rock dissolution progresses while the surface of the rock is preserved under coatings of silica glaze when a porosity of 37 47 is reached the weathering rind loses cohesion and spalls then the protective silica glaze starts to accrete again and another cycle begins cases 3 and 4 involve measuring rates of dissolution over thousands of years case 3 concerns rock dissolution in weathering rinds formed on ventifacted aplite boulders weathering rinds lost mass for the last 14 k y at a rate of 40 15 g m 2 k y and for the last 17 k y at a rate of 43 16 g m 2 k y dissolution rates increased over time to 67 23 g m 2 k y for the last 60 65 k y case 4 addresses the classic topic of which variable is most important in chemical weathering temperature precipitation or microenvironment in situ measurements of plagioclase dissolution in 3 k y old basalt flows reveal that warmer temperatures enhance rates of plagioclase dissolution by about 0 07 c when precipitation and microenvironment are controlled plagioclase dissolution increases as precipitation increases at higher elevations even though temperature decreases however microenvironment is a more important control on plagioclase dissolution organic rich positions under lichens weather two to seven times faster than adjacent organic poor positions away from epilithic organisms and rock coatings rates of rock weathering are often established indirectly by measuring the erosion of weathered material in contrast this microscopic method measures only in situ weathering conventional measures of rock weathering usually involve units for example depth of weathering pits or thickness of weathering rinds that are not readily comparable to other data in contrast cases 3 and 4 illustrate that in situ measurements of rock and mineral porosity can yield data on mass weathered per unit area over time this information is comparable to mass balance approaches in watershed and soil based weathering research

terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the himalayan orogen ladakh range northern india terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the ladakh range of the transhimalaya the glacial stages that have been identified are the indus valley glacial stage dated at older than 430 ka the leh glacial stage occurring in the penultimate glacial cycle or older the kar glacial stage occurring during the early part of the last glacial cycle the bazgo glacial stage at its maximum during the middle of the last glacial cycle and the early holocene khalling glacial stage the exposure ages of the indus valley moraines are the oldest observed to date throughout the himalayan orogen we observe a pattern of progressively more restricted glaciation during the last five glacial cycles likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation a possible explanation is that uplift of himalayan ranges to the south and or of the karakoram mountains to the west of the region may have effectively blocked moisture supply by the south asian summer monsoon and mid latitude westerlies respectively alternatively this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the pleistocene

sources of strontium and calcium in desert soil and calcrete the carbon cycle significance of soil carbonate fluxes is subject to large uncertainties because it is not clear precisely how much calcium is derived from atmospheric sources compared with that from the chemical weathering of silicate minerals in the petrocalcic horizon calcrete of a pleistocene soil from the usda scs desert project area near las cruces nm approximately 1 5 g ca cm 3 has been added with an associated expansion of the profile of200 strontium isotope values for the labile cations and carbonate from the a b and k soil horizons have 87 sr 86 sr values that range from 0 7087 to 0 7093 similar to the values for easily soluble local dust and rain the parent material non calcareous camp rice alluvial sediment has a 87 sr 86 sr ratio of0 7165 mixing calculations indicate a minimum atmospheric contribution to soil carbonate calcium of 94 the more likely scenarios indicate at least 98 of the ca originated from atmospheric input the variations in 87 sr 86 sr ratios of soil silicate 0 7131 to 0 7173 are consistent with weathering of volcanogenic sediments and neoformation of clay minerals in the petrocalcic horizon moreover the sr isotope data suggest that 50 70 of silicate in the uppermost 25 cm of the profile could be atmosphere derived the isotopic composition of labile strontium in the a horizon and the mass distribution of silicon and calcium indicate that the uppermost portion of the profile is the present zone for the release of cations due to silicate weathering steady state models of the whole profile yield a sr weathering flux ranging from200 to 400 m gc m 2 ma 1 the results indicate that both the present day and long term contribution of calcium from silicate weathering is less than 2 of that supplied from the atmosphere and confirm that desert soil formation is not a significant sink for atmospheric carbon 1999 elsevier science b v all rights reserved

lacustrine sedimentation in a semiarid alpine setting an example from ladakh northwestern himalaya abstract the lamayuru lacustrine strata in ladakh typify many of the carbonate rich pleistocene alpine lakes found in the semiarid environment of the northern himalaya created by a 200 m thick landslide the lake was in existence by at least 35 000 yr ago and may have persisted until 500 1000 yr ago represented in the center by thin turbidites and laminated muds the lacustrine sedimentation along the lake margins and low relief deltas characteristically displays a marked contrast between 1 clastic lenses representing rapid sporadic matrix poor debris flows and periglacial inputs from the alpine slopes and 2 abundant diverse shallow water biologically dominated carbonate strata among which organism rich chalky beds and oncolithic and encrusted stem rich strata predominate resemblances of the lamayuru lacustrine strata and their setting to those of former lakes throughout areas north of the greater himalayan crest suggest that the alpine semi arid environment would favor diversified spacially restricted carbonate sedimentation punctuated by occasional clastic influxes such a depositional regime contrasts strongly with that found immediately south of the himalayan crest where more humid conditions promote a more continuous clastic influx into intramontane lakes

evidence for transport of bedload in waves analysis of fluvial sediment samples in a small upland stream channel abstract data pertaining to the transport of fluvial sediment sampled in detail during a five hour long event in a small upland stream channel in the extremely arid southern negev are presented considerations based on comparative evaluations of water discharge stream power total and fractional sediment concentration and total and fractional sediment discharge suggest that bedload transport in channels of even very small upland catchments practically devoid of continuous alluvial cover takes place in waves which are not a priori related to any water discharge characteristic but rather reflect some intrinsic feature of watershed dynamics such as slope channel topographic contrasts or fluvial bifurcation the regular spacing of pools and riffles and of gravel bars in the more alluvial reaches downstream may therefore be initiated from upstream

the effect of oblique rain on inclined surfaces a nomograph for the rain gauge correction factor inclined rainfall leads to errors in the assessment of effective precipitation in areas with rugged relief this affects many hydrological studies such as hydrological forecasts water erosion determination of conditions for flash flood formation determination of cropping conditions etc in this paper a nomograph is presented for the rain gauge correction factor cgau by which rainfall measured in a standard horizontal rain gauge pgau may be corrected to obtain the rainfall flux actually received on the inclined surface under study pact cgau pgau the correction factor is assumed to be a function of wind with constant wind velocity type of rainfall and inclination and orientation of the sloping surface with respect to the oblique rain

mechanical and hydraulic resistance relations in crust topped soils abstract the formation of soil surface crusts leads to increased mechanical and hydraulic resistances in this study changes and relationships of both resistances under simulated sprinkle irrigation or rainfall and sprinkle followed by flooding were examined results indicated that a silt loam soil developed a thicker surface crust than a clay soil for any given kinetic energy ke crusts as thick as 3 9 and 2 6 mm formed on the silt loam and clay soils respectively mechanical resistance r m increased with increasing ke where the effect was greater in the silt loam and was attributed to intrinsic resistance and crust thickness steady state infiltration rate i was much lower in crusted clay than crusted silt loam soil changes of both r m and i closely followed changes in crust thickness z c thicker crusts showed more resistance against external force than thinner crusts due to more extended particle interlocking obtained functions indicated that the effect of thickness on strength was more significant in the lower range of crust thickness the effect of z c on i strongly followed a negative power function for both soils with higher i in the silt loam soil mechanical resistance showed high sensitivity to crusting and remained responsive to increasing severity change of r m in the silt loam soil was steeper than that of the clay soil r m of the silt loam soil increased from 0 5 n non crusted to 43 n highest ke with a relative change rel o r m of 86 for clay r m increased from 0 77 n to 22 n producing a rel o r m of 28 6 trends were consistent when evaluated relative to the lowest applied ke rel 1 r m where r m increased under highest ke about 6 9 and 4 7 times for the silt loam and clay soils respectively hydraulic resistance r h increased with increasing treatment intensity and was higher in the clay soil both r m and the work of resistance r w showed highly significant relationships with r h the silt loam soil displayed greater r w for any given r h although r h was markedly higher in the clay soil the rate of change was greater in the silt loam soil infiltration rate appeared highly sensitive to increased crusting particularly in the clay soil the i r h relationship strongly followed the negative power function i a r h b relative changes in i under ponding showed reduction factors of 130 and 180 relative to original soils and of approximately 23 and 28 times relative to the least intense treatment for the silt loam and clay soils respectively relative changes in r m correlated positively while rel i correlated negatively with rel r h in power equations the change of transmission zone suction u with r h fitted the function a r h m where a and m were constants characteristic of the soil using a function of the form k a n the characteristic constants a and n were determined as 0 174 and 3 01 for the silt loam and 1 367 and 1 61 for the clay soil and the characteristic k functions were obtained

crustal structure from three dimensional gravity modeling of a metamorphic core complex a model for uplift santa catalina rincon mountains arizona gravity modeling shows that the observed fluctuations in gravity over the catalina rincon metamorphic core complex of southeastern arizona are caused primarily by shallow crustal density contrasts the wilderness suite granites the probable source of a 20 mgal low over the central part of the core complex may extend to depths of 7 12 km below the surface seismic refraction information is consistent with the existence of a deep crustal root under the catalina rincon core complex we hypothesize that the voluminous wilderness suite granites are related to a crustal thickening event that built the root in early tertiary time modeling of flexural isostatic uplift resulting from an excess crustal root predicts two episodes of uplift for the catalina rincon metamorphic core complex 1 low relief flexural uplift in the middle tertiary and 2 complete uplift precipitated by high angle basin and range faulting at 10 15 ma the uplift and exposure of core complexes therefore can be an isostatically driven process that occurs in regions of locally thickened crust

sediment sources and sediment transport by rill flow and interrill flow on a semi arid piedmont slope southern arizona summary in this study sediment transport by rill flow and interrill flow on a piedmont hillslope were compared four experiments ranging in duration from 10 to 30 minutes were conducted under simulated rainfall delivered at 80 mm h 1 on a 18 35m runoff plot located on a gentle piedmont slope near tombstone southern arizona we observe that while the sediment concentration is similar size of sediment transported is considerably coarser in interrill flow than in rill flow sediment transport by interrill flow on thee piedmont slopes is influenced by the nature of splash wash interactions as flow concentration increases downslope the proportion of splash detached particles which reach competent threads of overland flow is reduced because raindrop detachment is aselective for size ranges up to several mm and the competence of sediment transport by interrill flow is enhanced by raindrop impact rather coarse material is transported sediment transport in rill flow is strongly influenced by overland flow input from upslope and above all the scour and fill processes which occur in the rills because of local deposition of sediment derived from upslope in the rills the reduced surface transport of splash detached particles from the adjacent contributing area to the rills and the selective nature of flow detachment relatively finer particles are transported in the rills on the basis of a clastic sediment budget evaluated for the bifurcation rill system we estimate that on a per storm basis 0 to 56 of the total sediment exported by the rill system is derived from sources in the rills however this result is strongly influenced by the sequence of events overall apart from some well established factors we suggest that sediment availability the degree of flow concentration and the propensity of scour and fill processes in the rills profoundly influence sediment transport on the experimental plot

morphological characterization of soil crust development stages on an experimental field abstract crust development on a loamy aquic hapludalf near paris was studied in an experimental field to which various fertilizers and amendments had been applied these treatments over a period of 57 years had induced a range of organic matter contents and exchangeable cation percentages the macroscopic aspects of the soil surface was closely monitored during crusting and microscopic characterization was carried out at every main crust development stage crusting followed a general pattern 1 sealing of the soil surface by a structural crust 2 development of a depositional crust even in the sodic plot where the depositional crust appeared especially early the structural crust developed first the change from the first stage to the second one mainly depended on a decrease in infiltrability due to the structural crust properties that induced micro runoff and puddling under rainfall structural crust development seemed to involve a coalescing process due to raindrop impact when moistening decreased soil cohesion this process developed much faster in the sodic than in the limed plot morphology of the depositional crust in particular microbedding and sorting could be related to the hydrodynamic behaviour of the soil surface abundance size and duration of puddles

late quaternary valley infill and dissection in the indus river western tibetan plateau margin abstract the indus one of earth s major rivers drains large parts of the nw himalaya and the transhimalayan ranges that form part of the western tibetan plateau margin in the western himalayan syntaxis where local topographic relief exceeds 7 km the indus has incised a steep bedrock gorge at rates of several mm yr 1 upstream however the upper indus and its tributaries alternate between bedrock gorges and broad alluvial flats flanked by the ladakh and zanskar ranges we review the late quaternary valley history in this region with a focus on the confluence of the indus and zanskar rivers where vast alluvial terrace staircases and lake sediments record major episodes of aggradation and incision new absolute dating of high level fluvial terrace remnants using cosmogenic 10 be optically and infrared stimulated luminescence osl irsl indicates at least two phases of late quaternary valley infilling these phases commenced before 200 ka and 50 20 ka judging from terrace treads stranded 150 m and 30 40 m above modern river levels respectively numerous stacks of lacustrine sediments that straddle the indus river 200 km between the city of leh and the confluence with the shyok river share a distinct horizontal alignment constraints from irsl samples of lacustrine sequences from the leh spituk area reveal a protracted lake phase from 177 ka to 72 ka locally accumulating 50 m thick deposits in the absence of tectonic faulting major lithological differences and stream capture we attribute the formation of this and other large lakes in the region to natural damming by large landslides glaciers and alluvial fans the overall patchy landform age constraints from earlier studies can be reconciled by postulating a major deglacial control on sediment flux valley infilling and subsequent incision that has been modulated locally by backwater effects of natural damming while comparison with pleistocene monsoon proxies reveals no obvious correlation a late or post glacial sediment pulse seems a more likely source of this widespread sedimentation that has partly buried the dissected bedrock topography overall the long residence times of fluvial alluvial and lacustrine deposits in the region 500 ka support previous studies but remain striking given the dominantly steep slopes and deeply carved valleys that characterise this high altitude mountain desert recalculated late quaternary rates of fluvial bedrock incision in the indus and zanskar of 1 5 0 2 mm yr 1 are at odds with the longevity of juxtaposed valley fill deposits unless a lack of decisive lateral fluvial erosion helps to preserve these late pleistocene sedimentary archives we conclude that alternating 10 4 yr long phases of massive infilling and incision have dominated the late quaternary history of the indus valley below the western tibetan plateau margin

surface crusting of volcanic ash deposits under simulated rainfall explosive volcanic eruptions can have severe impacts on watershed hydrology among them surface crusting of volcanic ash fallout following rainfall has been shown to favour runoff erosion and lahar initiation it may also hamper seed emergence and depress plant growth however ash crust formation is poorly understood reconstructed ash deposits were subjected to simulated rainfall to investigate the microscale morphological modifications of the ash deposit surface in response to raindrop impact ash samples from three volcanic eruptions mt merapi mer indonesia eyjafjallajokull eyja iceland and san cristobal sc nicaragua with different particle size distributions and soluble salt contents were used in the experiment microcraters and micropeaks formed on the surface of all ash deposits after rainfall initiation this was accompanied by fine material also referred to as micromass accumulation in the form of one or several layers a few tens to hundreds of micrometres thick such morphological changes point to structural crust formation the crusts consisted of a thin layer of tightly packed clay and silt size ash particles sc overlain by loose coarser materials in micro craters mer or by an almost continuous coarse grained layer eyja in all cases the surface crust had a reduced porosity compared with the bulk material depending on ash particle size crusting was governed by splash compaction and vertical sorting mer vertical particle sorting eyja or compaction sc no samples showed evidence of particle cementation through secondary salt precipitation our results shed new light on the mechanisms responsible for post depositional crusting of a natural ash deposit

late quaternary geomorphic scenario due to changing depositional regimes in the tangtse valley trans himalaya nw india abstract records from the tangtse valley in the trans himalaya reveal depositional history since 48 ka with fluvial aggradation followed by incision lacustrine sediment fill and later incision varied sedimentary architecture with fluvial episodes intervened by lacustrine pulses flood events colluvial and glacial activity are preserved the valley is located west of the pangong tso bangong co one of the largest lakes in tibet which has served as a spillway flooding and damming the entire tangtse valley resulting in the formation of a lake today pangong tso consists of five basins separated by shallow sills and is fed by snow melt documentation based on 14 c and osl chronologies of the sediment sections throughout the valley reveals evidence of a sixth basin of pangong tso toward west occupying the present day tangtse valley between 9 6 5 1 ka this event coincides with periods of high lake levels in tibet china as well as intensified monsoon periods over the indian subcontinent a fluvial regime around 48 ka and 30 21 ka with comparatively arid conditions and dry phases interspersed by flooding is documented the valley has been incised to depths of 40 50 m in the upper part and to 130 m in the lower part the incision rate ranges from 0 3 to 1 2 mm yr 1 in the upper part and reaches as high as 10 8 mm yr 1 in the lower valley much of the incision took place between 22 and 9 6 ka although repeated sediment fill incision cycles in the valley from 30 22 ka 22 9 6 ka 9 6 5 1 ka 5 1 ka and even to present time were observed

geomorphological response to an extreme flood a case from southeast spain on 28 29 september 1980 an extreme storm of 150 mm of rain in c 5 hours caused a flash flood near tabernas in a semi arid area in southern spain with the rainfall total approximating the mean annual rainfall the recurrence interval is estimated to be 25 100 years flood peak discharges have been estimated from a mountain source area across an alluvial fan and the geomorphological response to the storm described channel adjustment differed between channels in the fanhead trench and those unconfined channels on the fan surface the implications of the spatial pattern of erosional an depositional feaures for landform adjustment in semi arid regions are discussed

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

soil slip debris flow localized by site attributes and wind driven rain in the san francisco bay region storm of january 1982 abstract gis analysis at 30 m resolution reveals that effectiveness of slope destabilizing processes in the san francisco bay area varies with compass direction nearly half the soil slip debris flows mapped after the catastrophic rainstorm of 3 5 january 1982 occurred on slopes that face s to wsw whereas fewer than one quarter have a northerly aspect azimuthal analysis of hillside properties for susceptible terrain near the city of oakland suggests that the skewed aspect of these landslides primarily reflects vegetation type ridge and valley alignment and storm wind direction bedrock geology soil expansivity and terrain height and gradient also were influential but less so the role of surface curvature is not wholly resolved normalising soil slip aspect by that of the region s nnw striking topography shifts the modal azimuth of soil slip aspect from sw to se the direction of origin of winds during the 1982 storm but opposite that of the prevailing wnw winds wind from a constant direction increases rainfall on windward slopes while diminishing it on leeward slopes generating a modelled difference in hydrologically effective rainfall of up to 2 1 on steep hillsides in the oakland area this contrast is consistent with numerical simulations of wind driven rain and with rainfall thresholds for debris flow activity we conclude that storm winds from the se in january 1982 raised the vulnerability of the bay region s many s facing hillsides most of which are covered in shallow rooted shrub and grass that offer minimal resistance to soil slip wind driven rainfall also appears to have controlled debris flow location in a major 1998 storm and probably others incorporating this overlooked influence into gis models of debris flow likelihood would improve predictions of the hazard in central california and elsewhere

rain splash of dry sand revealed by high speed imaging and sticky paper splash targets 1 rain splash transport of sediment on a sloping surface arises from a downslope drift of grains displaced ballistically by raindrop impacts we use high speed imaging of drop impacts on dry sand to describe the drop to grain momentum transfer as this varies with drop size and grain size and to clarify ingredients of downslope grain drift the splash of many grains involves ejection of surface grains accelerated by grain to grain collisions ahead of the radially spreading front of a drop as it deforms into a saucer shape during impact for a given sand size splash distances are similar for different drop sizes but the number of displaced grains increases with drop size in proportion to the momentum of the drop not infiltrated within the first millisecond of impact we present a theoretical formulation for grain ejection which assumes that the proportion of ejected grains within any small azimuthal angular interval dq about the center of impact is proportional to the momentum density of the spreading drop within dq and that the momentum of ejected grains at angle q is on average proportional to the momentum of the spreading drop at q this formulation consistent with observed splash distances suggests that downslope grain transport involves an asymmetry in both quantity and distance more grains move downslope than upslope with increasing surface slope and on average grains move farther downslope this latter effect is primarily due to the radial variation in the surface parallel momentum of the spreading drop surface parallel transport increases approximately linearly with slope

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet

modern extreme storms and the rainfall thresholds for initiating debris flows on the hyperarid western escarpment of the dead sea israel intense rainstorms cause debris flows on escarpments in hyperarid environments in contrast with more temperate environments there have been no direct observations on rainfall intensities and durations required for initiating debris flows in hyperarid environments here we report rainfall volume and intensities acquired by gauge and radar measurements for two successive storms along the hyperarid the first of the two analyzed storms occurred on 2 november 1995 during this storm two convective cells rained sequentially within a 5 h period at the lower reaches of the nahal david and the nahal arugot that dissects the western escarpment of the dead sea israel this storm triggered debris flows in 38 small 2 and high gradient drainage basins along the escarpment total rainfall volume and spatial distribution were determined by 10 cumulative rain gauges that were also used to calibrate rainfall intensity distributions from radar data for this storm region and landscape rainfall intensities exceeding 30 mm h for a duration of 1 h were required to initiate debris flows a second storm in the same area on 17 18 october 1997 allowed the evaluation of the results determined from the 1995 storm in this second more regional storm maximum rainfall intensities were 19 27 mm h for a duration of 45 min these values lower than the 30 mm h minimal threshold defined in the previous storm are consistent with the occurrence of only three debris flows the small number of debris flows resulted from the concentration of the highest intensities of rainfall on the desert plateau and not directly on top of the canyon walls most first to third order basins draining the dead sea escarpment contain evidence of zero to three late holocene 30 mm h and durations of at least 1 h the small number of debris flows that has occurred during the late holocene indicates that such events are rare at the scale of individual drainage basins

the mechanism of 234u238u activity ratio enhancement in karstic limestone groundwater departamento de petrologia e metalogenia universidade estadual paulista campus de rio claro unesp sao paulo

asymmetrical erosion and morphological development of the central ladakh range northern india abstract variations in erosion were quantified across the topographically and morphometrically asymmetrical central ladakh range in nw india to elucidate erosion and sediment transfer processes across space and time and to gain insight into how mountains erode and evolve morphometric analysis and 10 be cosmogenic nuclide analysis of 14 fluvial sediment samples from active channels in six catchments conducted across the mountain range constrains 100 ka timescale erosion rates for catchments on the northern side of the mountain range and are between 56 12 and 74 11 m ma while catchments on the southern side of the mountain range to between 20 3 and 39 8 m ma for the last 300 ka maximum elevation from swath analysis across the range shows a strong correlation with the elas of 382 contemporary glaciers the higher erosion rate to the north likely relates to tectonic tilting of the central ladakh range and to active rock uplift on the northern side of the range along the karakoram fault morphometric analysis shows that the maximum and average elevations increase at nearly the same rate on a catchment scale across the central ladakh range with higher elevation on the northern side this suggests that greater erosion on the northern side of the range is not keeping pace with rock uplift moreover long term denudational unloading does not play a significant role in the tectonic tilting of the central ladakh range

quaternary geology tectonics and distribution of palaeo and present fluvio glacio lacustrine deposits in ladakh nw indian himalaya a study based on field observations abstract the ladakh region of the northwestern indian himalaya is rich in quaternary deposits but it has not received much attention previous quaternary research in the region has focused on the glacial sequences and only some scattered data of the lacustrine deposits are available this article addresses the reconstruction of the palaeo lacustrine deposits and the present day lakes and their distribution in the ladakh region the region was under the influence of tectonic activity and cold climate during the late quaternary times tectonic activity at 50 000 years bp 35 000 years bp and 25 000 years bp has been recorded we report the presence of three major lakes in the region in the late quaternary these formed due to the damming of the indus river and its tributaries by debris avalanches initiated mainly by tectonic activity along the indus suture shyok suture and the karakoram fault these are the spituk leh palaeolake formed 50 000 years bp the lamayuru palaeolake dated to 35 000 years bp in the indus valley and the khalsar palaeolake 60 km in length in the shyok valley vast exposures of the palaeolake deposits ranging from 25 to 150 m in thickness are reported spituk section 25 m lamayuru section 110 m and khalsar 150 m and hundri 100 m and which have a wide lateral extent a glacial lake basin at bhaktpur city north of baralacha la is now completely filled the tsokar lake has been subdivided into smaller units now and the water level is lowering other lakes in the region e g pangong tso tso morari the twin kyun tso lakes are confined to the western side of the study area limited chemical weathering rapid erosion and cold climatic conditions in late quaternary times are suggested by the stable illite values in the lamayuru section four levels of palaeoseismic structures convolute structures sand dykes intraformational folds micro faulting are present in the khalsar section and at three levels in the tirit section at shyok nubra confluence palaeoseismic activity was also prevalent after 25 000 years bp as is evident from the three levels of palaeoseismic structures in the younger sediments