the effects of soluble salts on the threshold shear velocity of fine sand wind tunnel tests were carried out to investigate the effects of two soluble salts nacl and kci on the threshold shear velocity of a well sorted fine sand a sensitive laser monitoring system was used to detect initial grain motion during the tests results indicate that even small amounts of soluble salt can significantly increase the threshold velocity of the sand because of cement like bonds formed between grains that tend to hold individual particles in place however with increasing concentration the salt crystal growth causes the initially smooth sand surface to develop an irregular frothy texture which also directly affects the threshold shear velocity this is indicated by increased scatter of data on the threshold shear velocity surface salt concentration plots for both nacl and kcl although data scatter is evident significant exponential relationships do exist between threshold shear velocity and surface salt concentration in each case

magnetic susceptibility anisotropy strain and progressive deformation in permian sediments from the maritime alps france abstract the relationships among magnetic susceptibility anisotropy finite strain and progressive deformation have been studied in permian red shales and slates of the maritime alps southeastern france these rocks contain deformed reduction spots which serve as finite strain indicators the magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of the deformation path derived from strain measurements the magnetic fabric changes progressively from oblate to prolate and back to oblate as deformation increases the quantitative relationships between natural strain and magnetic anisotropy in these rocks have been determined they differ between the less and more deformed areas perhaps due to a change in deformation mechanism accompanying an increase in metamorphism the relationships provide a rapid means of strain determination using magnetic measurements but their variation emphasizes the need for local structural control

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

longevity of aeolian megaripples abstract megaripples are distinguished from regular ripples by their larger dimensions and bimodal grain size distributions the interplay between wind grain size and ripple morphology height and wavelength controls their development two main mechanisms limit megaripple height the first megaripple flattening due to winds that are above the fluid threshold of the coarse grains destroys the armoring layer of the megaripple the second is megaripple erosion by the impacts of fast moving fine saltating grains that propel the coarse grains constituting the armoring layer for any given wind regime and grain size distribution the potential megaripple dimensions are limited by these two mechanisms here we study the first mechanism and estimate the duration of strong winds sustained above the fluid threshold needed to flatten megaripples strong gusts of wind in contrast cannot destroy the megaripples but can cause ripple migration based on data from previous works on megaripples we find a scaling law between the ripple morphology and the coarse mode of grains at the crest using this scaling relation allows us to calculate the wind velocity and duration needed for megaripple flattening in general the coarser the particles at the megaripple crest the stronger the wind needed to flatten the megaripples moreover the greater the strength of the wind required to flatten the megaripples the lower the recurrence probability taken together these findings increase the longevity of megaripples we apply the results for a megaripple field in the southern arava valley israel

the effect of wind speed averaging time on the calculation of sand drift potential new scaling laws abstract drift potential dp is a key factor used to quantify aeolian sand transport and it is often used for predicting wind erosion and dune mobility under climate change scenarios it is proportional to the mean of the cube of the wind speed at a 10 m height when that wind speed is above 6 2 m s 12 knots a speed threshold above which sand can be transported by the wind dp depends on the temporal resolution and the averaging time of the wind velocity measurements usually either a 10 min or 1 h mean wind speed is used to calculate the dp although different studies have used different averaging periods for calculating the mean wind speed and consequently the dp here we perform a comprehensive analysis of an extensive long term wind speed database from different locations around the world and from reanalysis data sources and show that dp decreases with the averaging time of the wind speed the decrease of dp versus the averaging time interval can be approximated by a stretched exponential function in addition the relative decrease of dp as a function of the maximum dp is smaller for high wind speed sites this result is a consequence of the fact that high dp sites are characterized by longer clusters of successive wind speed events above the threshold velocity they are thus less affected by the time averaging process interestingly the clusters lengths decay exponentially with wind speed and faster for low dp sites our new results have important implications for calculating the effective dp and for better estimating the biases that result from using wind data with different averaging times which is a common problem in aeolian research we also found an approximate linear relation between dp and the wind power that is close to the analytic approximation for the relation between the two this new finding has many important applications since it will allow one to calculate dp from wind power data and vice versa in addition it implies that the same scaling laws found for dp also exist for the wind power

characteristics of near surface wind regimes in the taklimakan desert china abstract using wind data from 17 meteorological stations distributed throughout the taklimakan desert we described the characteristics of the desert s wind regimes and analyzed the spatial and temporal variations in wind direction and sand drift intensity the near surface wind regimes were closely related to general atmospheric circulation patterns and the surrounding topography there are two prevailing wind directions in the desert in general the eastern part of the desert is mainly affected by ne winds and the western part is affected by nw winds in the area towards the center of the desert but not around its edges the monthly mean wind velocity is strongly correlated with the monthly mean temperature with the exception of ruoqiang on the eastern edge of the desert the drift potential dp is less than 200 vu and the desert thus belongs to a low energy environment based on fryberger s classification in addition most parts of the desert have an rdp resultant dp dp value greater than 0 4 suggesting that the wind regimes have mainly unimodal or bimodal characteristics in contrast with the sand drift intensity which was highest in the north and east parts of the desert the highest frequency of sand dust storms occurred at the southwestern margin of the desert this results primarily from the differences of dust content on ground surfaces and land use types

fabric development and metamorphic evolution of lower palaeozoic slaty rocks from the rocroi massif french belgian ardennes new constraints from magnetic fabrics phyllosilicate preferred orientation and illite crystallinity data abstract this paper presents new results of a petrofabric study from cambrian slates cropping out within the anchi epimetamorphic core of the rocroi massif ardennes variscan fold thrust belt of northern france and southern belgium this study includes measurements of the anisotropy of the isothermal remanent magnetisation airm and the phyllosilicate preferred orientation it completes the previous results of anisotropy of magnetic susceptibility ams and of magnetic mineralogy which were obtained in 47 sites situated in and around this massif these new data allow the characterisation of the different subfabrics carried by the ferromagnetic minerals metamorphic pyrrhotite and magnetite and the paramagnetic matrix fe rich phyllosilicates combined with some illite crystallinity data measured throughout the massif the petrofabric measurements evidence a polyphase tectonometamorphic evolution a major variscan compressional event is evidenced inducing the growth of highly anisotropic pyrrhotite coarse grained hematite and phyllosilicates by contrast the magnetite grains display a less well organised fabric due to the existence of an inherited orientation pattern in agreement with recent metamorphic studies it argues for an early diastathermal metamorphic event developed during a devonian crustal scale extension

reactivation of supply limited dune fields from blowouts a conceptual framework for state characterization aeolian dune fields mantle the earth in both vegetated stable and unvegetated active states changes in state are poorly understood in particular little is known about reactivation devegetation from a vegetated state available evidence indicates that dune reactivation can be driven by changes in aridity increased wind speed fire biogenic disturbance human disturbance or a combination of the previous how these controls fit together and define the reactivation potential of dune fields is presently unknown here we develop a framework to describe reactivation potential for a specific case presently vegetated supply limited dune fields that develop blowouts under a unidirectional wind we first define a conceptual model of blowout expansion and then split the functions of vegetation in a stable dune field into i maintenance of a protective skin and ii blowout suppression we model reactivation as disturbance breaking through the protective skin which forms a blowout that is either i suppressed by colonizer species or ii capable of advancing downwind and reactivating part of the dune field the capacity for disturbance to break through the protective skin is a function of disturbance magnitude area and resistance of the skin the blowout suppression capacity of a dune field is a function of sediment flux blowout depth related to geomorphology and colonizer species vitality by plotting a given dune field with two variables protective skin breach rate and blowout suppression capacity we define four states i stable ii blowout dominated iii reactivating or iv stable but disturbance susceptible we reinforce the conceptual model with qualitative examples and discussion of experiments on grassland stabilized dunes in canada overall our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields

complex spatial feedbacks of tephra redistribution ice melt and surface roughness modulate ablation on tephra covered glaciers tephra fallout from the 2011 grimsvotn eruption onto svinafellsjokull iceland created an ice ash landscape of a type that is rarely studied but is nevertheless common in glaciovolcanic regions we used terrestrial laser scanning tls to measure ice surface topography and absorption at high spatial resolution confirming ablation rates either reduce or increase under thick insulating and thin reduced albedo ash deposits respectively fourier transform analysis of the tls data identified that a three fold increase in aerodynamic roughness was attributable to an increase in larger 0 2m surface features moreover tls measurements revealed the importance of ash redistribution by meltwater in generating differential melting which modifies roughness and ash patchiness such that the net effect of these spatial ash ice feedbacks was to reduce ablation rates by up to 59 the modulating effects of these previously undocumented feedbacks on ablation rates are therefore significant and must be correctly parameterized if ashcovered glacier mass balances are to be predicted correctly

spectral signatures of characteristic spatial scales and nonfractal structure in landscapes 1 landscapes are sometimes argued to be scale invariant or random surfaces yet qualitative observations suggest that they contain characteristic spatial scales we quantitatively investigate the existence of characteristic landscape scales by analyzing two dimensional fourier power spectra derived from high resolution topographic maps of two landscapes in california in both cases we find that spectral power declines sharply above a frequency that corresponds roughly to hillslope length implying that the landscape is relatively smooth at finer scales the spectra also show that both landscapes contain quasiperiodic ridge and valley structures and we derive a robust measure of the ridge valley wavelength by comparing the spectra with the statistical properties of spectra derived from randomly generated topography we show that such uniform valley spacing is unlikely to occur in a random surface we describe several potential applications of spectral analysis in geomorphology beyond the identification of characteristic spatial scales including a filtering technique that can be used to measure topographic attributes such as local relief at specific scales or in specific orientations

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

temporal dynamics of flooding evaporation and desiccation cycles and observations of salt crust area change at the bonneville salt flats utah abstract the bonneville salt flats bsf in utah is a dynamic saline playa environment responding to natural and anthropogenic forces over the last century the saline groundwater from below bsf has been harvested to produce potash via evaporative mining mostly used as agricultural fertilizers while the surface halite crust has provided a significant recreational site for land speed racing perceptions of changes in the salt crust through time have spurred debates about land use and management however little is known about the timescales of natural change as the salt crust responds to climatic parameters that drive flooding evaporation and desiccation fed cycles that control surface salt growth and dissolution climate data over the last 30 years are examined to identify annual patterns in surface water balance at bsf to identify annual and seasonal climate constraints on fed cycles landsat satellite data from 1986 to the present are used to map the areal extent of the surface halite salt crust at bsf at the end of the desiccation season between august 15 and october 30 annually overall the observed area of the desiccation stage bsf halite crust has varied from a maximum of 156 km2 in 1993 to a minimum of 72 km2 in 2014 with an overall trend of declining area of halite observed over the 30 years of analysis climatic variables that influence fed cycles and seasonal salt dissolution and precipitation have also varied through this time period however the relationship between surface water fluxes and salt crust area do not clearly correlate suggesting that other processes are influencing the extent of the salt intra annual analyses of salt area and weather illustrate the importance of ponded surface water wind events and microtopography in shaping a laterally extensive but thin and ephemeral halite crust examination of annual to decadal changes in salt crust extent and environmental parameters at bsf provides insights into the processes driving change and the sustainability of land use in this dynamic environment

the dynamism of salt crust patterns on playas playas are common in arid environments and can be major sources of mineral dust that can influence global climate these landforms typically form crusts that limit evaporation and dust emission modify surface erosivity and erodibility and can lead to over prediction or underprediction of 1 dust emission potential and 2 water and heat fluxes in energybalance modeling through terrestrial laser scanning measurements of part of the makgadikgadi pans of botswana a southern hemisphere playa that emits significant amounts of dust we show that over weeks months and a year the shapes of these surfaces change considerably ridge thrusting of 30 mm week and can switch among continuous ridged and degraded patterns ridged pattern development changes the measured aerodynamic roughness of the surface as much as 3 mm week the dynamic nature of these crusted surfaces must be accounted for in dust entrainment and moisture balance formulae to improve regional and global climate models

subtle stretching lineation revealed by magnetic fabric of callovian oxfordian black shales french alps abstract the anisotropy of magnetic susceptibility ams of callovian oxfordian black shales from the subalpine massifs of the french alps has been measured the magnetic susceptibility of these formations originates from ferromagnetic titanomagnetite and paramagnetic phyllosilicates illite and chlorite although the magnetic fabric is complicated by the interaction of planar and linear structural elements and the presence of variable amounts of minerals two types of lineation are preserved a stretching lineation which exhibits counterclockwise rotation as a result of deformation from south to north and an intersection lineation parallel to the fold axis this set of new structural data together with semiquantitative analysis of ams is in agreement with the geodynamic evolution of the western alps

relationship of spaced cleavage to folds and thrusts in the idaho utah wyoming thrust belt the idaho utah wyoming thrust belt of the rocky mountain cordillera preserves structures that developed at very shallow levels of the crust t 200 c the geometry of major structures is well documented and synorogenic conglomerates record the timing of movement on major thrusts spaced cleavage and pencil fracturing are developed within micrites of the jurassic twin creek formation the cleavage developed dominantly by pressure solution early in the deformation history of each thrust sheet aided by elevated temperatures and pressures in areas where increased overburden resulted from emplacement of earlier overriding sheets cleavage within any sheet is well developed in the area covered by the pre erosional extent of the previous sheet forelandward from this area cleavage intensity decreases drastically thermal modelling of the sheets agrees well with temperature estimates from illite crystallinity studies on material from the cleavage planes cleavage is axial planar to small folds and formed concurrently with small scale buckle folds and contraction faults during the early history of movement on each thrust however cleavage strongly fans about large scale folds formed later during movement suggesting passive rotation of cleavage with bedding during the later stages of thrust history the rotated cleavage may also be folded and overprinted by a second weaker cleavage during a second ramping or during movement on a later lower thrust cross folding may also develop as a result of lateral ramping thus complex patterns of interfering folds multiple cleavages and associated fiber filled fractures may be produced during motion on a single thrust fault and so magnify the problem of correlating cleavages and deciphering multiple deformations

estimating aerodynamic roughness over complex surface terrain 1 surface roughness plays a key role in determining aerodynamic roughness length zo and shear velocity both of which are fundamental for determining wind erosion threshold and potential while zo can be quantified from wind measurements large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach alternative approaches therefore seek to relate zo to morphological roughness metrics however dust emitting landscapes typically consist of complex small scale surface roughness patterns and few metrics exist for these surfaces which can be used to predictzofor modeling wind erosion potential in this study terrestrial laser scanning was used to characterize the roughness of typical dust emitting surfaces playa and sandar where element protrusion heights ranged from 1 to 199mm over which vertical wind velocity profiles were collected to enable estimation of zo our data suggest that although a reasonable relationship r 2 0 79 is apparent between 3 d roughness density and zo the spacing of morphological elements is far less powerful in explaining variations in zo than metrics based on surface roughness height r 2 0 92 this finding is in juxtaposition to wind erosion models that assume the spacing of larger scale isolated roughness elements is most important in determining zo rather our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting zo this finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments

the spatial and temporal variability of sand erosion across a stabilizing coastal dune field this study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in israel these were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline vegetation cover was estimated based on aerial photographs and landsat satellite images whereas the relative height was based on a digital elevation model these variables were calculated for the area upwind south west of the erosion pins at various lengths ranging from 15 to 400 m nine geomorphologic units were defined five related to active units and four to stabilized units in active units at least 65 of the temporal variance in the annual absolute changes in sand level was explained by the index of resultant drift potential with most of the sand movement occurring during winter storms local rainfall had no apparent impact on sand mobility due to the low coincidence of sand carrying winds and rainfall in israel during the passage of frontal cyclones as for the spatial variables only a weak correlation was found between sand mobility with the distance from the coastline r 2 18 rather sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100 200 m upwind the values of soil adjusted vegetation index were significantly negatively correlated with annual absolute changes r 2 40 whereas the relative height was significantly positively correlated r 2 36 applying a multiple regression model 68 of the spatial variability in sand mobility was explained the resulting map of sand activity clearly shows that at this stage of the stabilization process most of the dunes are now disconnected and movement of sand grains from the beach or between the dunes is very limited these methods can be applied into spatial and temporal models of sand mobility thus assessing the impact of different management practices on coastal dunes

thrust surface geometry implications for thrust belt evolution and section balancing techniques abstract the application of modern concepts of thrust tectonics to orogenic belts has yielded many detailed restorable sections thrusts generally restore with a staircase geometry onto the undeformed stratigraphic template since the work of rich 1934 it has been generally assumed that thrusts have propagated with a staircase trajectory and that hangingwall structures result from the movement of the thrust sheet up footwall ramps however thrusts often cut through previously folded strata with a smooth trajectory smooth trajectory thrusts can be identified from footwall geometry and strain state once a smooth trajectory thrust has been identified it is insufficient to produce a balanced deformed section and its restored counterpart sequential balanced sections must be constructed reversing the deformation history the restoration of thrusts to a staircase trajectory has no mechanical significance as the thrust is merely acting as a marker if restored back beyond the time at which it propagated thrust ramps are not necessarily actual steps in the thrust surface they are often just zones where the thrust cuts through bedding in a smoothly curving trajectory ductile deformation in thrust belts can reduce bed length at depth thus removing the need for structures which are necessary to preserve constant bed lengths ductile deformation in the internal zones of orogenic belts renders the construction of balanced sections in these zones highly problematical

the influence of deformation mechanisms on magnetic fabrics in weakly deformed rocks abstract magnetic fabrics of weakly deformed rocks are not simply correlated with the principal finite strain directions depositional magnetic fabrics persist at 30 shortening where the rocks are deformed by particulate flow grain boundary sliding rocks with a spaced stylolitic cleavage believed to be formed by pressure solution and shortened by 20 50 have maximum susceptibility parallel to the intersection of cleavage and bedding this type of magnetic fabric is attributed to the interference of a depositional magnetic fabric between cleavage surfaces with a tectonic magnetic fabric in the cleavage surfaces

the hydrochemistry of a semi arid pan basin case study sua pan makgadikgadi botswana this study presents results on the fluid and salt chemistry for the makgadikgadi a substantial continental basin in the semi arid kalahari the aims of the study are to improve understanding of the hydrology of such a system and to identify the sources of the solutes and the controls on their cycling within pans sampling took place against the backdrop of unusually severe flooding as well as significant anthropogenic extraction of subsurface brines this paper examines in particular the relationship between the chemistry of soil leachates fresh stream water salty lake water surface salts and subsurface brines at sua pan botswana with the aim of improving the understanding of the system s hydrology occasionally during the short wet season december march surface water enters the saline environment and precipitates mostly calcite and halite as well as dolomite and traces of other salts associated with the desiccation of the lake the hypersaline subsurface brine up to tds 190 000 mg l is homogenous with minor variations due to pumping by botash mine botswana ash pty ltd which extracts 2400 m 3 of brine h from a depth of 38 m notable is the decrease in tds as the pumping rate increases which may be indicative of subsurface recharge by less saline water isotope chemistry for sr 87 sr 86 sr average 0 722087 and s d 34 s average 34 35 suggests subsurface brines have been subject to a lithological contribution of undetermined origin recharge of the subsurface brine from surface water including the nata river appears to be negligible

correlation of strain and the anisotropy of magnetic susceptibility in the onaping formation evidence for a near circular origin of the sudbury basin abstract measurements of finite strain the anisotropy of magnetic susceptibility the magnetic carrier of the susceptibility and fieldwork have been carried out in the onaping formation of the sudbury basin ontario the magnetic fabric indicates that changes in the magnitude and type of magnetic susceptibility ellipsoids closely mirror the changing pattern of deformation from northwest to southeast across the onaping formation outcrops a quantitative correlation has been established between finite strain measurements and the magnetic susceptibility results and this allows the number of available strain measurements to be extended by more than 500 samples the finite strain results suggest a deformation path in which the onaping formation was first affected by nw se directed horizontal layer parallel shortening which produced an upright tectonic cleavage subsequently components of overthrust nw directed simple shear were superimposed upon the already deformed rocks of the onaping formation the result of removing the strain according to the sequence of superimposed deformations revealed by the deformation path suggests that the sudbury basin was nearly circular in shape prior to its deformation consequently a major objection to the meteorite impact theory for origin of the sudbury structure is eliminated

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

surface roughness and bulk heat transfer on a glacier comparison with eddy correlation more than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice the results proved to be extremely sensitive to measurement height which is difficult to define precisely on the hummocky terrain of a glacier therefore aerodynamic roughness lengths were estimated from the microtopography of the surface yielding 2 46 mm for ice and 5 5 mm for snow despite the indeterminate nature of the profile analysis it did support the view that the thermal roughness length must decrease as the roughness reynolds number increases a relationship which has been modelled in the literature good agreement between bulk transfer estimates and eddy correlation measurements of fhe sensible heat flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length

form drag in rivers due to small scale natural topographic features 2 irregular sequences 1 the size shape and spacing of small scale topographic features found on the boundaries of natural streams rivers and floodplains can be quite variable consequently a procedure for determining the form drag on irregular sequences of different sized topographic features is essential for calculating near boundary flows and sediment transport a method for carrying out such calculations is developed in this paper this method builds on the work of kean and smith 2006 which describes the flow field for the simpler case of a regular sequence of identical topographic features both approaches model topographic features as two dimensional elements with gaussian shaped cross sections defined in terms of three parameters field measurements of bank topography are used to show that 1 the magnitude of these shape parameters can vary greatly between adjacent topographic features and 2 the variability of these shape parameters follows a lognormal distribution simulations using an irregular set of topographic roughness elements show that the drag on an individual element is primarily controlled by the size and shape of the feature immediately upstream and that the spatial average of the boundary shear stress over a large set of randomly ordered elements is relatively insensitive to the sequence of the elements in addition a method to transform the topography of irregular surfaces into an equivalently rough surface of regularly spaced identical topographic elements also is given the methods described in this paper can be used to improve predictions of flow resistance in rivers as well as quantify bank roughness

heating during thrust faulting in the rocky mountains friction or fiction abstract measurement of the levels of organic maturation below and within shear zones of thrust faults in the rocky mountains has revealed no general thermal metamorphism that can be attributed to faulting with the exception of very localized areas with few exceptions the vitrinite reflectance values obtained are in the range expected if the maximum level of organic maturation was produced as a result of increasing temperature during progressive burial accompanying sedimentation only at marias pass evidence has been found to suggest additional maturation as a result of post orogenic burial below the thrust sheets anomalously high vitrinite reflectances obtained from the lewis thrust mcconnell thrust coleman thrust and two unnamed thrusts are restricted to very narrow films immediatly adjacent to or within the shear zone which considering any reasonable thermal conductivity indicates elevated temperatures were very short lived the anomalously high vitrinite reflectances within these films when compared to laboratory heated coals suggest temperatures in the order of 350 650 c were locally generated during faulting such high temperatures are considered to have been generated during stick slip faulting at macro asperities or at ramps on the fault plane where local and possibly transient high frictional stresses existed the absence of evidence for extensive frictional heating supports previous arguments that stable sliding and or low frictional stress must exist during thrusting

the stabilizing role of bonding agents on the entrainment of sediment by wind well sorted fine sand pretreated with varying concentrations of two soluble salts mgcl2 and cacl2 was tested for threshold shear velocity in a recirculating wind tunnel these tests demonstrate that even relatively low surface salt concentrations can significantly increase threshold shear velocity however the relationships between surface salt concentration and threshold shear velocity for the two salts were not significantly different which is similar to the results for monovalent chlorides presented by nickling ecclestone a general relationship between threshold shear velocity and total surface soluble salt content is presented

applications of spaceborne radar laboratory data to the study of aeolian processes aerodynamic roughness z0 is an important parameter in studies of sand and dust transport as well as atmospheric circulation models aerodynamic roughness is a function of the size and spacing of surface roughness elements and is typically determined at point locations in the field from wind velocity profiles because field measurements require complex logistics z0 values have been obtained for very few localities if radar can be used to map z0 estimates can be obtained for large areas in addition because aerodynamic roughness can change in response to surface processes e g flooding of alluvial surfaces radar remote sensing could obtain new measurements on short timescales both z0 and the radar backscatter coefficient 0 are dependent on topographic roughness at the submeter scale and correlation between these two parameters was developed based on radar data obtained from aircraft airsar the spaceborne radar laboratory srl afforded the opportunity to test the correlation for data obtained from orbit srl data for sites in death valley california lunar lake nevada and gobabeb namibia were correlated with wind data and compared with previous radar z0 relations correlations between 0 and z0 for l band 24 cm hv h vertically and v vertically polarized modes l band hh and c band 5 6 cm hv compare favorably with previous studies based on these results maps of z0 values were derived from srl data for each site demonstrating the potential to map z0 for large vegetation free areas from orbit using radar systems

deformation of a foreland carbonate thrust system sawtooth range montana an analysis of mesoscale faulting associated with thrust belt development was completed along a transect crossing several foreland thrust sheets of the central sawtooth range montana at a regional scale a balanced cross section of the central sawtooth range constrained by well seismic and surface data indicates a minimum of 60 horizontal shortening of the upper paleozoic carbonate bank sequence accommodated by a forward developing thrust system subsurface data delineates a 4 westward dipping precambrian basement and westward thickening of the precambrian belt supergroup major decollements within the central sawtooth range are present at the base of the devonian jefferson formation in the lower mississippian allan mountain limestone and in the cretaceous colorado group within the diversion french norwegian and beaver thrust sheets of the central sawtooth range deformation has been partitioned into arrays of meter to decimetersized faults that constitute brittle deformation zones bdzs bdz thickness is directly related to fault displacement but is not related to fault trajectories or subsequent foreland imbrication the ratio of bdz thickness to displacement is nearly constant with bdz thicknesses ranging from 65 m to 200 m for faults whose displacements range from 2 km to 5 km the bdzs of each thrust sheet can be separated into three regions defined by differences in fault diversity fault intensity and fault kinematics proportionally the locations of boundaries between regions within the bdzs are remarkably constant for each of the four thrust sheets studied indicating that the bdzs widen uniformly during thrust sheet emplacement bdz bases are characterized by an interlocking network of faults that exhibit great diversity and accommodate mesoscale cataclastic flow bdz bases are dominated by oblique slip faults whereas the middle and upper regions of bdzs are dominantly dip or strike slip faults in all regions of a bdz localized zones of contractional extensional or more commonly transport parallel strike slip faults bounded by bedding plane detachments are present fault length m2 of outcrop decreases logarithmically to zero from a maximum of 4 m m2 across the french and norwegian bdzs zones of intense faulting alter this general pattern of decreasing fault intensity in the diversion and beaver thrust sheets

a note on the use of the fryberger method for evaluating potential sand transport by wind the fryberger method provides a useful and accessible way of evaluating potential sediment transport by wind in this method an equation is used to estimate relative rates of sand transport expressed as drift potential from measurements of wind velocity however the values of drift potential obtained through the calculations are dependent upon the units in which wind velocities are expressed this paper highlights some of the confusion this dependence can cause and aims to clarify the ways in which values of drift potential can be interpreted

persistence in intra annual snow depth distribution 2 fractal analysis of snow depth development 1 we present an analysis of high resolution laser scanning data of snow depths of three different slopes in the wannengrat catchment introduced in part 1 using omnidirectional and directional variograms for three specific terrain features cross loaded slopes lee slopes and windward slopes a break in scaling behavior was observed in all subareas which can be seen as the roughness scale of bare earth terrain which is modified by the snow cover in the wind protected lee slope a different scaling behavior was observed compared to the two wind exposed areas the wind exposed areas have a smaller ordinal intercept a smaller short range fractal dimension d and a larger scale break distance l than the wind protected lee slope snow depth structure inherits characteristics of dominant nw storms which results e g in a trend toward larger break distances in the course of the accumulation season this can be interpreted as a result of surface smoothing at increasing scales similar scaling characteristics were obtained for two different years at the end of the accumulation season since snow depth structure is altered strongly by nw storms this inter annual consistency may strongly depend on their frequency in an accumulation period with the analysis of directional variograms anisotropies of fractal parameters were detected which were related to dominant wind directions

strain variation in thrust sheets across the sevier fold and thrust belt idaho utah wyoming implications for section restoration and wedge taper evolution abstract although strain in fold and thrust belts is typically inhomogeneous on the largest scale strain within thrust sheets shows regular patterns the strain which is a quantitative measure of the deformation of any thrust sheet is independent of the translation of the sheet the internal deformation can be represented by a deformation profile the change in shape during thrusting of a fault perpendicular line which can then be used to unstrain the sheet during restoration in cross section balancing deformation profiles in well studied thrust sheets show regular geometric patterns and compatibility constraints can be used to minimize the data needed to define the profiles in other sheets from the geometry of deformation profiles and direct field observations the most important component of internal deformation of thrust sheets in many fold and thrust belts is early layer parallel shortening lps this can be removed in a straightforward manner during restoration and significantly affects the geometry i e taper of the restored section original basin wedge taper may have important implications for the mechanical evolution of fold and thrust belts thus changes in original basin taper resulting from strain removal may affect significantly the way in which we interpret the evolution of a fold and thrust belt in an area

characteristics of wind blown sand in the region of the crescent moon spring of dunhuang china based on the detailed wind data this paper aims to investigate wind regime drift potential and the movement of mega dunes at the crescent moon spring an important scenic spot in western china and to clarify the dominant factors that control sand transport in this region the results of this paper revealed that the dominant wind directions at the spring were nw and sw the spring region belonged to a low energy wind environment the wind regime and sand drift potential were hugely influenced by local topography and the regional atmospheric circulation intensified the complexity of their variations besides the movement of the southern and northern mega dune towards the spring greatly endangered the preservation of this scenic spot these results provide insights into the characteristics of wind blown sand at the crescent moon spring that will guide efforts to control sand damages

magnetic fabrics in l s tectonites how many specimens abstract single large blocks 10 30 kg of homogeneously strained fine grained slate or schist with homogeneous fabrics reveal subtle but sometimes significant variations in magnetic fabric from large numbers up to 100 of closely spaced cylindrical cores traditional samples of three to six cores per block or per site may suffice for low precision regional determinations of fabric orientations if suitably fine grained and homogeneous however for the most precise definition of anisotropy of magnetic susceptibility axes ams small sample sizes

fault dating in the canadian rocky mountains evidence for late cretaceous and early eocene orogenic pulses fault rocks from the classic rocky mountain foreland fold and thrust belt in southwestern canada were dated by ar analysis of clay grain size fractions using x ray diffraction quantification of the detrital and authigenic component of each fraction these determinations give ages for individual faults in the area illite age analysis the resulting ages cluster around 72 and 52 ma here called the rundle and mcconnell pulses respectively challenging the traditional view of gradual forward progression of faulting and thrust belt history of the area the recognition of spatially and temporally restricted deformation episodes offers field support for theoretical models of critically stressed wedges which result in geologically reasonable strain rates for the area in addition to regional considerations this study highlights the potential of direct dating of shallow fault rocks for our understanding of upper crustal kinematics and regional tectonic analysis of ancient orogens

climate surface pore water interactions on a salt crusted playa implications for crust pattern and surface roughness development measured using terrestrial laser scanning sodium accumulating playas also termed sodic or natric playas are typically covered by polygonal crusts with different pattern characteristics but little is known about the short term hours dynamics of these patterns or how pore water may respond to or drive changing salt crust patterning and surface roughness it is important to understand these interactions because playa crust surface pore water and roughness both influence wind erosion and dust emission through controlling erodibility and erosivity here we present the first high resolution 10 3m hours co located measurements of changing moisture and salt crust topography using terrestrial laser scanning tls and infra red imagery for sua pan botswana maximum nocturnal moisture pattern change was found on the crests of ridged surfaces during periods of low temperature and high relative humidity these peaks experienced non elastic expansion overnight of up to 30 mm and up to an average of 1 5 mm night during the 39 day measurement period continuous crusts on the other hand showed little nocturnal change in moisture or elevation the dynamic nature of salt crusts and the complex feedback patterns identified emphasise how processes both above and below the surface may govern the response of playa surfaces to microclimate diurnal cycles

terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics smith m w cox n j bracken l j 2011 terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics hydrological processes 25 6 842 860

terrestrial laser scanning in geology data acquisition processing and accuracy considerations terrestrial laser scanning or lidar is a recent innovation in spatial information data acquisition which allows geological outcrops to be digitally captured with unprecedented resolution and accuracy with point precisions and spacing of the order of a few centimetres an enhanced quantitative element can now be added to geological fieldwork and analysis opening up new lines of investigation at a variety of scales in all areas of field based geology integration with metric imagery allows 3d photorealistic models to be created for interpretation visualization and education however gaining meaningful results from lidar scans requires more than simply acquiring raw point data surveys require planning and typically a large amount of post processing time the contribution of this paper is to provide a more detailed insight into the technology data collection and utilization techniques than is currently available the paper focuses on the workflow for using lidar data from the choice of field area and survey planning to acquiring and processing data and finally extracting geologically useful data because manufacturer specifications for point precision are often optimistic when applied to real world outcrops the error sources associated with lidar data and the implications of them propagating through the processing chain are also discussed

an improved bathymetric model for the modern and palaeo lake eyre abstract here we demonstrate the applicability of using altimetry data and landsat imagery to provide the most accurate digital elevation model dem of australia s largest playa lake lake eyre we demonstrate through the use of geospatial techniques a robust assessment of lake area and volume of recent lake filling episodes whilst also providing the most accurate estimates of area and volume for larger lake filling episodes that occurred throughout the last glacial cycle we highlight that at a depth of 25 m lake mega eyre would merge with the adjacent lake mega frome to form an immense waterbody with a combined area of almost 35 000 km2 and a combined volume of 520 km3 this would represent a vast water body in what is now the arid interior of the australian continent the improved dem is more reliable from a geomorphological and hydrological perspective and allows a more accurate assessment of water balance under the modern hydrological regime the results presented using glas icesat data suggest that earlier historical soundings were correct and the actual lowest topographic point in australia is 15 6 m below sea level the results also contrast nicely the different basin characteristics of two adjacent lake systems lake eyre and lake frome

magnetic anisotropy reveals neogene tectonic overprint in highly strained carbonate mylonites from the morcles nappe switzerland magnetic anisotropy reveals neogene tectonic overprint in higly strained carbonate mylonites from the morcles nappe switzerland

magnetic anisotropy rock fabrics and finite strain in deformed sediments of sw sardinia italy abstract although some empirical relationships have been established between the anisotropy of magnetic susceptibility ams and the state of finite strain in studies from specific geologic areas the mechanisms governing correlations are not well understood a comparative study has been made in order to elucidate the ams strain relationship by investigating mineral preferred orientations and the responsible microstructural deformation processes detailed analyses are presented from low grade metamorphic slates of a palaeozoic sequence exposed in the variscan of sw sardinia rock magnetic experiments suggest that paramagnetic minerals dominate the ams in these rocks excellent agreement was found between magnetic fabrics and lattice preferred orientations 001 of mica and chlorite determined from x ray texture goniometry measurements depending on the oblate or prolate ellipsoidal shape of anisotropy the minimum principal axes of ams and x ray textures can coincide with the poles to slaty cleavage or the maximum principal axes can coincide with the bedding cleavage intersection respectively the measured ams and x ray textures only partially reflect the finite strain determined from deformed micro pebbles and reduction spots axial orientations of magnetic fabrics mica and chlorite preferred orientations and finite strain ellipsoids are generally in good agreement depending on development of oblate or prolate fabric ellipsoidal shapes linear correlations can be established for magnitudes of minimum and intermediate axes of the ams and finite strain ellipsoids but shape comparisons are complex microstructural studies by scanning electron microscopy sem indicate that the preferred orientation of the phyllosilicates is caused by different grain scale deformation mechanisms such as kinking micro folding and preferential growth thus magnetic fabrics and mineral preferred orientations evidently result from different deformation mechanisms than the finite strain they reflect the heterogeneous deformation due to micro mechanical reorientation processes of mineral grains while finite strain reflects the homogeneous deformation accommodated cumulatively by the strain markers

models of strain variation in nappes and thrust sheets a review abstract strain within nappes and thrust sheets can be modelled using simple boundary conditions an original rectangular prism of material resting on a thrust plane is considered to be subject to various pure and simple shear components operating parallel to the thrust deformation gradient tensors are determined for the models and solutions found for the principal strains a two dimensional model considers heterogeneous simple shear combined with a stretch in the direction of shear simple shear zones arise as a special case where 1 recumbent fold nappes characteristic of gravitational collapse can be modelled with 1 and thrust sheets with layer parallel shortening and folding with differential transport of nappes gives rise to additional wrench type shears solutions for the principal strains in this type of model are found and used to interpret side wall ramps and steep zones parallel to nappe movements by including a stretch in the transport direction these differential transport models produce prolate strains 1 and oblate strains finally a brief consideration of bending strains produced in a sheet passing over a ramp indicates reversals in the shear direction during the strain history these predict possible crenulation of early thrust fabrics at ramps

effects of tectonic deformation on the remanent magnetization of rocks paleomagnetic investigations have usually been impossible in deformed rocks because of the effects of distortion on the remanent magnetization vector deformation produces a magnetic anisotropy in rocks which can deflect the remanence away from the minimum susceptibility axis however the assumption that the intersection points of great circles joining these two directions represent an improved estimate of the undisturbed remanence is invalid because the amount of the deflection of each remanence is not really known anisotropy of magnetic susceptibility ams provides a quantitative basis for strain determination the principal axes of the magnetic anisotropy ellipsoid have the same directions as those of the strain ellipsoid a linear relationship between the normalized principal susceptibility differences and the logarithmic strains has been found in several rock types if the correlation method used is valid ams observations can be used to establish the magnitudes and directions of the principal strains strain modifies bedding planes and realigns the grains that carry magnetic remanence compensation for deformation requires application of a modified bedding tilt correction and correction of the remanent vector for distortional strain the effects of strain on bedding can be corrected using passive marker theory attempts to compensate for distortional strain by treating the remanent vector as a passive marker have proved inconclusive during deformation linear and planar elements deflect away from the axis of maximum shortening the passive marker correction shifts the remanent vectors toward the local shortening axis for the site and reduces the directional scatter tests of the passive marker method in strongly deformed rocks resulted in a remanence distribution dominated by the shortening axis directions the passive marker model becomes inapplicable when the deformation results in recrystallization of the rock matrix

the correlation of magnetic anisotropy with strain in the chelmsford formation of the sudbury basin ontario abstract a quantitative correlation has been established between finite strain and the anisotropy of magnetic susceptibility ams in sandstones of the precambrian chelmsford formation of the sudbury basin ontario investigations of the progressive acquisition of isothermal remanent magnetization and its destruction with reverse field and thermal demagnetization as well as microscopic examination of polished thin sections show that both pyrrhotite and magnetite are present in the sandstone measurements of the ams have been carried out at 16 sites distributed throughout the chelmsford formation outcrop considerable variation in the shapes of the magnetic susceptibility ellipsoids axes k max k int k min exists within each site with the k max and k int axes contained in the cleavage planes where developed the magnitudes of the magnetic susceptibility axes have been quantitatively correlated with strain measurements carried out by clendenen et al this issue two different strain to magnetics correlations have been carried out between the site mean strain determined using deformed concretions and the mean values of the ams at each site and between individual specimen strain values determined at the microscopic scale and the individual specimen ams in both cases separate correlations were made between strain long intermediate and short axes and their corresponding magnetic k max k int and k min axes at 10 sites the site mean strain values were derived from strain analysis of the concretions and at an additional 6 sites the site mean strain values were derived from the ams to strain correlation 527 individual cores were converted to equivalent strain values using the ams structural correlation of individual specimens this study extends the use of ams methods to include strain determination in sandstones and provides an order of magnitude increase in the available number of such data for further structural analysis

dust emission from wet and dry playas in the mojave desert usa the interactions between playa hydrology and playa surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion the production of evaporite minerals during evaporative loss of near surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas observations that characterize the texture mineralogic composition and hardness of playa surfaces at franklin lake soda lake and west cronese lake playas in the mojave desert california along with imaging of dust emission using automated digital photography indicate that these kinds of surface sediment are highly susceptible to dust emission the surfaces of wet playas are dynamic surface texture and sediment availability to wind erosion change rapidly primarily in response to fluctuations in water table depth rainfall and rates of evaporation in contrast dry playas are characterized by ground water at depth consequently dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water although not the dominant type of global dust salt rich dusts from wet playas may be important with respect to radiative properties of dust plumes atmospheric chemistry windborne nutrients and human health published in 2007 by john wiley sons ltd

comparison of fry strain ellipse and ams ellipsoid trends to tectonic fabric trends in very low strain sandstone of the appalachian fold thrust belt abstract in moderately to highly strained sandstones both the long axis of the bedding parallel finite strain ellipse as calculated by the normalized fry method and the projection of the long axis of the ams ellipsoid on the plane of bedding align well with local structural grain trends of cleavage folds and faults this relationship implies that results of both 2d fry and ams analyses represent the local layer parallel tectonic strain component do both methods provide comparable results for very low strain sandstone e g

anisotropy of magnetic susceptibility ams and diamagnetic fabrics in the durness limestone nw scotland anisotropy of magnetic susceptibility ams and diamagnetic fabrics in the durness limestone nw scotland

composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics housen b a richter c and van der pluijm b a 1993 composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics tectonophysics 220 1 12 magnetic fabrics from rocks with multiple mineral preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and or orientations of the individual mineral fabrics and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks these criteria include 1 the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics and 2 the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases composite magnetic fabrics are observed in the shales and slates of the martinsburg formation lehigh gap pennsylvania modeling of the ams anisotropy of magnetic susceptibility and arma anhysteretic remanent magnetization anisotropy behavior constrains the relative degree of anisotropy of the bedding parallel and cleavage parallel fabrics in particular arma model results allow a good estimate of magnetite fabric strength we conclude that in the presence of composite magnetic fabrics quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric such determinations require knowledge of the mineral s that are responsible for the measured magnetic fabric and their behavior during deformation

wind regimes and aeolian transport in the great basin u s a abstract the modern great basin of the interior western united states is characterized by surface winds with considerable spatial and temporal variabilities wind records from the second half of the 20th century for 12 great basin localities analyzed with standard aeolian sediment transport methods developed elsewhere in the world reflect this complexity the drift potential dp for aeolian deposits is generally moderate dp 200 400 in the western great basin and weak dp 300 at the eastern edge of the great basin where the dominant prevailing wind direction is south southwesterly both dp and resultant drift direction rdd are consistent with synoptic meteorological observations of the evolution of cold fronts in the great basin meteorological observations show that effective winds to produce dunes are most commonly the result of late winter early spring cyclogenesis there has been considerable temporal variability of dp in the latter half of the 20th century most of the great basin has experienced decreasing wind strength since 1973 consistent with recent studies of wind strength in north america and elsewhere dune morphology matches both localized rdd and temporal variations in dp reasonably well in the great basin the results demonstrate that local topography can have an important influence on wind directionality thus providing a cautionary note on the interpretation of dune morphology in the paleoclimatic and stratigraphic record

morphodynamics and climate controls of two aeolian blowouts on the northern great plains canada blowouts are the most regionally pervasive active aeolian landform on the northern great plains of north america this study reports a long term investigation into the morphological development of two adjacent blowouts in a continental dune field the blowouts were monitored for a decade in the bigstick sand hills of southwestern saskatchewan canada topographic changes were determined from dense arrays of erosion pins in each blowout 1 per 4 m2 n 171 and 1 per 16 m2 n 150 pin measurements were made 16 times between may 1994 and may 2004 over the decade both blowouts expanded and more than doubled in volume differences in form flow interactions have caused the larger of the two blowouts to deposit more than a metre of sediment within the deflation basin and the smaller blowout to erode by more than a metre a negative feedback effect was triggered when the larger blowout reached a critical size around 1994 60 m 36 m 8 1 m length width height when sediment was no longer eroded from the deflation basin a positive feedback in the smaller blowout continues to facilitate erosion from the deflation basin monthly observations since 2002 indicate that aspect plays an important role in the development of these blowouts by creating a spatial asymmetry in sediment availability sediment is more readily available throughout the year on south facing slopes which receive greater insolation than north facing slopes and are often drier and more frequently thawed in this cold climate environment comparisons between climate data from a remote meteorological station 45 km to the southwest and sediment transport indices developed from the erosion pin data produced very few correlations significant at the 95 per cent confidence level nevertheless the signs of the correlation coefficients indicate that sediment erosion and deposition in both blowouts respond similarly to the following climate variables recorded at the remote station i the amount of precipitation ii the transport capacity of the wind and iii transporting winds from a directional wedge between 180 and 330 taken altogether the results from this study highlight the importance of climate and feedback effects in blowout development that may be extended to other blowouts in continental and coastal settings copyright 2006 john wiley sons ltd

morphological and sedimentary features of oblique zibars in the kumtagh desert of northwestern china abstract zibars are coarse grain armored low relief aeolian bedforms with a large spacing but without slipfaces little is known of their morphodynamic processes even though they are ubiquitous at upwind desert margins in this paper we describe the morphological and sedimentary features of oblique zibars in the northeastern kumtagh desert of china analyze the effective wind regime and discuss the significance of the coarse grained sediments for zibar morphology and sedimentary structures due to a mantle of coarse grains oblique zibars and nearby linear dunes respond to different effective wind regimes that result in the angle between their geomorphological trends topographic surveys showed that the spacing of the oblique zibars ranged between 130 5 and 357 5 m and that the height ranged between 0 6 and 3 0 m the oblique zibar surface is almost entirely covered by coarse sand and includes gravel with a particle diameter of up to 2 34 the poorly sorted positively to very positively skewed surface sediments with mean grain size ranging between 0 2 and 1 5 were characterized by a bimodal distribution the spacing between the oblique zibars is closely related to the coarsest 5th percentile of the surface sediments and can potentially be explained by a combination of the saturation length and minimum dune size theories in addition the protectionist theory combined with the surface creep and vibration of coarse grains which allows infiltration of finer materials between the grains may account for the alternating coarse and fine laminae in the oblique zibars

the effect of wind and precipitation on vegetation and biogenic crust covers in the sde hallamish sand dunes vegetation and biogenic crust covers play an important role in sand dune stabilization yet there is a lack of high temporal and spatial resolution data on sand dune cover a field experiment aimed at measuring the dynamics of biogenic crust and vegetation in sand dunes was conducted at the sde hallamish sand dunes in the northwestern negev desert israel from july 2008 to august 2010 the climate of the sde hallamish sand dunes is arid the mean annual precipitation over the past 13 years is 61 mm and the dunes are linear and partially stable mainly due to the presence of biogenic crust and partially due to the presence of vegetation in july 2008 10 10 m plots on the four dune habitats crest interdune north slope and south slope were treated as follows i removal of vegetation and biogenic crust ii removal of biogenic crust only iii removal of vegetation only iv partial removal of biogenic crust and vegetation and v control plot the surface coverage of sand biogenic crust and vegetation was monitored on a monthly basis using a remote sensing technique especially developed for the sde hallamish sand dunes it was found that strong wind events with durations of several days accounted for the coverage changes in biogenic crust and vegetation the response to precipitation was much slower in addition no rehabilitation of biogenic crust and vegetation was observed within the experiment time period the changes in biogenic crust cover were not necessarily related to changes in dune dynamics since often an increase in biogenic crust cover is a result of wind erosion that exposes old crust that was buried under the sand wind hardly erodes biogenic crust at all due to its high durability to wind action the sde hallamish dunes seem to have become more active as a result of a prolonged drought during the past several years the field experiment reported here indicates that biogenic crust cover exhibits large seasonal variations that are not necessarily related to the growth of new crust but rather to the exposure of old buried crust

floating brine crusts reduction of evaporation and possible replacement of fresh water to control dust from owens lake bed california summary owens lake california a saline terminal lake desiccated after diversion of its water source was formerly the single largest anthropogenic source of fugitive dust in north america over 100 billion m 3 yr 1 of fresh water are projected to be used for mandated dust control in over 100 km2 of constructed basins required to be wetted to curtail emissions an extensive evaporite deposit is located at the lake s topographic low and adjacent to the dust control basins because this deposit is non dust emissive it was investigated as a potential replacement for the fresh water used in dust control the deposit consists of precipitated layers of sodium carbonate and sulfate bathed by and covered with brine dominated by sodium chloride perennially covered with floating salt crust evaporation e rates through this crust were measured using a static chamber during the period of highest evaporative demand late june and early july 2009 annualized total e from these measurements was significantly below average annual precipitation thus ensuring that such salt deposits naturally remain wet throughout the year despite the arid climate because it remains wetted the evaporite deposit may therefore have the potential to replace fresh water to achieve dust control at near zero water use

application of a new in situ 3d laser scanner to study the scale effect on the rock joint surface roughness application of a new in situ 3d laser scanner to study the scale effect on the rock joint surface roughness

origin of orogenic remagnetizations in mississippian carbonates sawtooth range montana 1 paleomagnetic results are presented from mississippian madison group carbonates in the sawtooth range northwestern montana samples were collected from sites along two east west trending transects perpendicular to the thrust faults in the sun river canyon and in the north and south forks of the teton river and from three folds the madison group contains a widespread characteristic remanent magnetization chrm that resides in magnetite with southerly declinations and moderately steep up inclinations tilt test results suggest that the chrm is pretilting in the thrust sheets and teton anticline but syntilting in the clary coulee and swift dam folds the chrms all have the same characteristics and were probably caused by the same remagnetization event yet the tilt test results are different one explanation involves the difference in fold types between the teton anticline fault bend fold geometry and the clary coulee and swift dam folds fault propagation fold geometries the deformation that produced the two geometries could have caused variations in strain stress which may have altered an original pretilting into a syntilting chrm a mean paleopole for the three pretilting tilt test results 67 2 n 177 9 e a95 13 1 suggests remanence acquisition in the late jurassic early tertiary the chrm is interpreted as a chemical remanent magnetization crm geochemical studies indicate that the mississippian carbonates were altered by evolved fluids with radiogenic 87sr 86sr values and petrographic analysis indicates that hydrocarbons migrated through the carbonates the crm is interpreted to be related to alteration by one of these fluids

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

a comparison of the effectiveness of clast based finite strain analysis techniques to ams in sandstones from the sevier thrust belt wyoming abstract geological strain analysis of sedimentary rocks is commonly carried out using clast based techniques which rely on assumptions regarding clast shapes and orientations as well as distances between clast centres to evaluate the accuracy of these methods in low strain regimes we have compared strain analysis estimates to the anisotropy of magnetic susceptibility ams in sandstone samples from the wyoming salient the cordilleran mountain belt of north america is one of the world s classic foreland fold and thrust belts the sevier belt represents the thin skinned front of this orogenic event characterized by thrust faults and folds that shortened and translated sequences of devonian to cretaceous strata eastward deformation increases westward providing an ideal laboratory and geological setting to explore the potential correlation of anisotropy of magnetic susceptibility ams to clast based strain analyses studies attempting to define the relationship between ams and finite strain have been in vogue since the link between layer parallel shortening and ams was first established this relationship despite proven strong correlations between the ams tensors and tectonic directions is generally complicated by competing sub fabrics as well as the various magnetic anisotropy properties of the minerals contributing to the ams fabric even with these complications we conclude that ams is much more sensitive to incipient tectonic fabrics than clast based methods

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data

duplex structures and imbricate thrust systems geometry structural position and hydrocarbon potential duplexes and imbricate thrust systems form some of the most complex hydrocarbon traps in overthrust belts the geometry of a duplex is controlled by the ramp angle thgr and height hr the final spacing between adjacent thrusts a prime and the relative displacements on them d1 d2 for constant thgr and hr three different classes are recognized 1 independent ramp anticlines and hinterland sloping duplexes 2 true duplexes and 3 overlapping ramp anticlines imbricate thrust systems consist of several thrust faults each of which loses displacement upsection and eventually dies out by progressively transferring its displacement to a fold at its tip or by distributing it among several splays hybrid duplexes are ormed from systems of fault propagation folds that are subsequently carried over ramps so they have a more complex geometry and a greater structural relief these different types of thrust systems occur as outcrops and prospect scale structures and they define the regional structural styles of most fold and thrust belts second and third order duplexes and imbricate thrust systems occur in specific structural positions such as footwalls hanging walls and frontal zones of major thrust ramps and in cores of major anticlines several types of duplexes and imbricate thrust systems form important hydrocarbon traps examples include the system of independent anticlines of the turner valley and highwood oil and gas fields the hinterland sloping duplex consisting of the chestnut ridge sandy ridge system of the ben hur oil field the partly overlapping anticlines of the waterton and savanna creek gas fields and the completely overlapping anticlines of the rose hill oil field

the role of maximum wind speed in sand transporting events abstract a sand transporting event is the minimum unit of aeolian sand transport process to understand the role of maximum wind speed in such sand transporting events wind speeds were measured at a height of 2 m above the ground in the arid menggen and semi arid taibus banner regions in north china during 2009 and 2011 the sand transport flux of each sand transporting event was calculated based on theoretical equations then the relationships between the maximum wind speed and the average wind speed the duration and sand transport flux of sand transporting events were analyzed it was found that the maximum wind speed was proportional to the average wind speed of sand transporting events with a linear model fit and was also significantly correlated with the duration of sand transporting events with a power model fit the maximum wind speed was also positively correlated with sand transport flux of sand transporting events according to a power model the maximum wind speed could therefore represent both wind speed and the duration of sand transporting events and play a decisive role in the sand transport process of these events the sand transport flux of sand transporting events can be predicted rapidly and conveniently by monitoring maximum wind speed