multiscale bed form interactions and their implications for the abruptness and stability of the downwind dune field margin at white sands new mexico usa the downwind margin of white sands dune field is an abrupt transition from mobile aeolian dunes to a dune free vegetated surface this margin is also relatively stable over the past 60 years it has migrated several times more slowly than the slowest dunes within the dune field resulting in a zone of dune coalescence aggradation and along most of the margin development of a dune complex i e dunes superimposed on draas repeat terrestrial laser scanning surveys conducted over a 3 month period demonstrate that sediment fluxes within the dune complex decrease on approach to the margin computational fluid dynamics modeling indicates that this decrease is due in part to a decrease in mean turbulent bed shear stress on the lee side of the dune complex as a result of flow line divergence or sheltering of the lee side dunes by the stoss side of the dune complex conservation of mass demands that this decrease in bed shear stress causes aggradation we speculate that aggradation on the lee side of the dune complex further enhances the sheltering effect in a positive feedback contributing to the growth and or maintenance of the dune complex and a relatively abrupt and stable dune field margin our model and data add to a growing body of evidence that aeolian dune field patterns are influenced by feedbacks that occur at scales larger than individual dunes

multi spatial analysis of aeolian dune field patterns abstract aeolian dune fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales this study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on earth mars and titan within a single bedform type different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well organized pattern such as with the transition from protodunes to dunes additionally different types of bedforms such as ripples coarse grained ripples and dunes coexist at different spatial scales within a dune field analysis of dune field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform interpretations of environmental conditions from any scale of bedform however are limited to environmental signals associated with the response time of that bedform large scale dune field patterns integrate signals over long term climate cycles and reveal little about short term variations in wind or sediment supply wind ripples respond instantly to changing conditions but reveal little about longer term variations in wind or sediment supply recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune field patterns

the backus gilbert approach to the three dimensional structure in the upper mantle i lateral variation of surface wave phase velocity with its error and resolution summary the backus gilbert method is applied to obtain the phase velocity variations on a sphere from the measured phase velocity narrow peak kernels with radii of about 2000 km are obtained for almost everywhere on the sphere the phase velocity results are thus interpreted as an average within such regions the most trouble comes from the antipodal peak in the resolution kernel this is evaluated as contamination and is incorporated in the error estimation the total error which is a root mean square of contamination from the antipodal peak and statistical error estimated from the data covariance matrix is about 1 per cent of the phase velocity in the average earth model which is the preliminary reference earth model prem however there is about a factor of 2 variation of errors on the sphere maximum variations of phase velocity are about 3 4 per cent of the phase velocity in the average earth model and thus there still remain anomalies which exceed estimated errors the estimated errors correspond to one standard deviation under the assumptions of uncorrelated gaussian distribution for high confidence interval they show that statistically significant anomalies are scarce for the current data set generally love wave phase velocity maps show more resolved features than rayleigh wave maps and we can see in high confidence maps fast velocities in old oceans and old continents and slow velocities in tectonically active regions like the east pacific rise and various back arc regions

lateral heterogeneity and azimuthal anisotropy of the upper mantle love and rayleigh waves 100 250 s the lateral heterogeneity and apparent anisotropy of the upper mantle are studied by measuring rayleigh and love wave phase velocities in the period range 100 250 s spherical harmonic descriptions of the lateral heterogeneity are obtained for order and degree up to 1 m 10 slow regions are evident at the east pacific rise northeast africa tibet tasman sea southwestern north america and triple junctions in the northern atlantic and indian oceans fast regions occur in australia western pacific and the southern atlantic these features are also found by a completely different analysis based on the backus gilbert method the backus gilbert method also shows that the obtained phase velocities are averaged values within an area of about 2000 km radius and the errors are about 1 of the phase velocity in the zeroth order spherically symmetric earth inversion for azimuthal dependence shows that for low angular order the fast phase velocity directions seem to correlate well with the plate motion vectors however resolution analysis by the backus gilbert method shows that the current data do not have enough resolution for everywhere on the globe only a few regions currently have adequate azimuthal coverage thus confirmation of the above correlation requires a more complete data set

aeolian processes and features in cool climates this review concentrates on the characteristics of wind processes and products in cold lowland deserts its main aims are to show how difficult it can be to separate wind generated from water generated processes and features without detailed study of lamination types to suggest cold aeolian interpretations for some ancient pre quaternary rocks and to encourage students to revisit many ancient deposits with such interpretations in mind although upper quaternary and recent cold climate aeolian deposits have been studied for many years there are very few older examples described martian features are included since mars is now one of the most exciting areas of study

reply to comment by g etiope and g martinelli pieve santo stefano is not a mud volcano comment on structural controls on a carbon dioxide driven mud volcano field in the northern apennines

martian mud volcanism terrestrial analogs and implications for formational scenarios the geology of mars and the stratigraphic characteristics of its uppermost crust mega regolith suggest that some of the pervasively occurring pitted cones mounds and flows may have formed through processes akin to terrestrial mud volcanism a comparison of terrestrial mud volcanism suggests that equivalent martian processes likely required discrete sedimentary depocenters volatile enriched strata buried rheological instabilities and a mechanism of destabilization to initiate subsurface flow we outline five formational scenarios whereby martian mud volcanism might have occurred a rapid deposition of sediments b volcano induced destabilization c tectonic shortening d long term load induced subsidence and e seismic shaking we describe locations within and around the martian northern plains that broadly fit the geological context of these scenarios and which contain mud volcano like landforms we compare terrestrial and martian satellite images and examine the geological settings of mud volcano provinces on earth in order to describe potential target areas for piercement structures on mars our comparisons help to evaluate not only the role of water as a functional component of geological processes on mars but also how martian mud volcanoes could provide samples of otherwise inaccessible strata some of which could contain astrobiological evidence

effects of atmospheric conditions on wind profiles and aeolian sand transport with an example from white sands national monument quantifying aeolian sand transport rates relies upon the computation of the near surface shear velocity u determined from velocity profiles of the wind while it has been recognized that various conditions such as saltation surface roughness surface slope and atmospheric conditions have an effect on the velocity profile it is commonly assumed that measurements made above the surface will be representative of the near surface shear velocity airflow and temperature data collected over a flat substrate at white sands national monument in new mexico however show the significant effects that atmospheric conditions have on velocity profiles during the day when solar insolation is heating the surface atmospheric conditions in the lowest several metres become unstable resulting in enhanced convection and vertical mixing so that the velocity gradient changes little with height as a result the shear stress in this region of vertical mixing lessens while the near surface shear stress is increased because the higher wind speeds are now nearer the surface at night the near surface atmospheric conditions are stable thereby reducing convection and vertical mixing resulting in stratified airflow and increased shear velocity away from the surface unless this atmospheric effect is accounted for estimates of sediment transport rates may be in error by as much as a factor of 15 times when wind speeds are near threshold velocity at wind speeds approaching 10 ms1 at 5m above the surface this error in computing sediment transport is reduced to a factor of only two to three times and may be within the range of measurement error

variations in wind velocity and sand transport on the windward flanks of desert sand dunes the magnitudes of increases in wind velocity or speed up factors have been measured on the windward flanks of transverse and linear dunes of varying height on transverse dunes velocity speed up varied with dune shape and height for linear dunes speed up factors varied principally with wind direction relative to the dune with dune shape and dune height the main effect of velocity speed up on the windward flanks of dunes is to increase potential sand transport rates considerably in crestal areas this is greatest for large dunes with winds of moderate velocity blowing at a large angle to the dune changing ratios of base to crest sand transport rates on transverse dunes tend to reduce dune steepness as overall wind velocities increase on linear dunes the tendency for crestal lowering is counteracted by deposition in this area when winds reverse in a bi directional wind regime

anisotropy and shear velocity heterogeneities in the upper mantle long period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle the dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure the data are corrected for the effect of surface layers and both love and rayleigh waves are used shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km the shear wave velocity distribution to 200 km depth correlates with surface tectonics except in a few anomalous regions below that depth the correlation vanishes cold subducted material shows up weakly at 350 km as fast s wave anomalies in the transition region a large scale pattern appears with fast mantle in the south atlantic s anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones the pacific shows a nw se fabric

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

mapping convection in the mantle long period 100 250 sec love and rayleigh waves are used to map heterogeneity and azimuthal anisotropy in the upper mantle spherical harmonic descriptions of anisotropy up to l m 3 and 2 are derived azimuthal anisotropy obtains values as high as 1 there is good correlation of fast rayleigh wave directions with upper mantle return flow directions derived from kinematic considerations this is consistent with the a axis of olivine being aligned in the flow direction the main differences between the flow models and the rayleigh wave azimuthal variation maps occur in the vicinity of hotspots hawaii for example appears to perturb the return flow there is strong correlation of the geoid and surface wave velocity at l 4 and 5 slow regions at this scale are associated with geoid highs and high heat flow consistent with upwelling convective flow or with isostatically compensated regions of low density the correlation of azimuthal anisotropy with upper mantle return flow directions rather than with plate directions suggests that part of the return flow is in the upper mantle and this in turn implies a low viscosity channel

interrelations of mud volcanism fluid venting and thrust anticline folding examples from the external northern apennines emilia romagna italy 1 the present work aims to provide an example of connection between fluid seepage and fault fracture zones associated with compressional thrust folds surface fluid seepage along the pede apennine margin consists of mud volcanism and methane rich emissions showing an intimate link with thrust related folds dominant gaseous or ch4 bearing fluid emissions characterize thrust fold settings in which fluid escape from the main reservoir and source rock i e the marnoso arenacea flysch is not impeded by a seal layer conversely remarkable mud volcanism is closely linked to the presence of the impermeable ligurian units sealing the marnoso arenacea reservoir structural analyses focused on selected thrust folds exhibiting clear relations between surface seepage and brittle elements associated with the fold various scenarios potentially explaining mud volcanism and venting over the crestal region of the thrust related folds are discussed with respect to fluid pressure state and the development of second order fault and fracture sets that are observed to control surface fluid expulsion it is proposed that mud volcanism can be potentially triggered by first order fault failure cycles during which the overpressured fluid is released during faulting events past anomalous eruptions associated with strong earthquakes seem to support this hypothesis the relatively quiescent but continuous activity of the current pede apennine mud volcanoes could instead reflect a short lived leakage of overpressured fluids along permeable fractures faults expansion of methane contained in the rising mud may assist this process fundamentally

comparative characteristics of the black sea and mediterranean ridge mud volcanoes morphological and structural characteristics of the black sea and mediterranean ridge mud volcanoes studied during several unesco esf cruises of the r v gelendzhik 1991 1994 are compared on the basis of single and multi channel seismic and sidescan sonar observations morphologically three types of mud volcanoes were distinguished in the black sea and six types in the mediterranean they differ in size shape and presence of the mud flows some types from both localities are very similar to each other but in any case their deep structure is very distinctive this difference in deep structure is explained by their development in different geological conditions under an extensional regime with high terrigenous input in the black sea and under strong lateral compression on the mediterranean ridge

flow dynamics and sediment transport over a reversing barchan changli china abstract the flow and sediment transport over a reversing 6 9 m high barchan dune is examined on the changli gold coast in hebei province china wind velocity profiles are non logarithmic exhibit rapid accelerations up slope and display near surface jets at the dune crest and downwind lee slope from the windward lower slope to dune crest the wind speed at 5 cm height increased by 55 the windward slope is a slipface and therefore has a significantly greater gradient than most normal windward slopes and the magnitude of speed up is significantly greater speed up ratio of 5 25 the majority of sediment was transported in the 0 4 cm height above the bed range maximum total sediment flux occurred at the dune crest and was greater than the total flux from three other sites combined the leeward mid slope sedimentation rate is strongly influenced by the sediment plume streaming upwards and downwind from the actively reversing dune crest dunes in the process of reversing display quite different wind flow and sedimentation patterns than when the dune is in normal flow conditions

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

geochemistry of gases and waters discharged by the mud volcanoes at paterno mt etna italy approximately 20 km south of mt etna craters at the contact between volcanic and sedimentary formations three mud volcanoes discharge co2 rich gases and na cl brines the compositions of gas and liquid phases indicate that they are fed by a hydrothermal system for which temperatures of 100 150 c were estimated by means of both gas and solute geothermometry the hydrothermal system may be associated with co2 rich groundwaters over a large area extending from the central part of etna to the mud volcanoes numerous data on the he ch4 co2 composition of the gases of the three manifestations sampled over the past 5 years indicate clearly that variations are due to separation processes of a co2 rich gas phase from the liquid the effects of these processes have to be taken into account in the interpretation of the monitoring data collected for the geochemical surveillance of etna volcano

11 11 dune morphology and dynamics this chapter discusses the key types of sand dunes and how they can be classified and assesses the major controls on their development the processes of dune dynamics are reviewed leading to a discussion of the concept of equilibrium in solitary dune form recent advances in modeling are reviewed that show how interactions between dunes may result in equilibrium at the dune field scale rather than at the single dune scale

timescale dependence of aeolian sand flux observations under atmospheric turbulence 1 the transport of sand in saltation is driven by the persistently unsteady stresses exerted by turbulent winds based on coupled high frequency observations of wind velocity and sand flux on a desert dune during intermittent saltation we show here how observations of saltation by natural winds depend significantly on the timescale and method used for determining shear stress and sand flux the correlation between sand flux and excess shear stress stress above a threshold value systematically improves for longer averaging timescale t and is better for stress determined by the law of the wall versus the reynolds stress method fitting parameters for the stress flux relationship do not converge with increasing t which may be explained by the nonstationary nature of wind velocity statistics we show how it may be possible based on the scale dependent statistics of stress fluctuations to rescale saltation flux predictions for wind observations made at different timescales however our observations indicate hysteresis and time lags in thresholds for initiation and cessation of saltation which complicate threshold based approaches to predicting sediment transport at different timescales

structure and emplacement of mud volcano systems in the south caspian basin the term mud volcano system is coined to describe the set of structures associated with a constructional edifice mud volcano and feeder complex that connects the volcano to its source stratigraphic unit three dimensional 3 d seismic data from the south caspian basin are used to investigate the structural elements and evolution of these systems mud volcano systems initiate via early kilometer scale biconic edifices termed pioneer cones these are fed by fluidization pipes tens of meters in width subsequent kilometer scale mud volcanoes grew via persistent extrusion fed by numerous additional fluidization pipes injected in the country rock this subvolcanic intrusion complex creates a densely intruded cylindrical zone similar in cross section to gryphon swarms observed at an outcrop onshore wall rock erosion and compaction of the intruded zone leads to the collapse of a downward tapering cone enveloping the cylindrical zone capped by ring faults that define a kilometer scale caldera that downthrows the overlying mud volcano mud volcanoes get buried during basin subsidence and can look like intrusive laccoliths at first glance on seismic data reactivation of mud flow through a conduit system generates a stack of superimposed mud volcanoes through time large volcanoes continue to dewater during burial and may locally remobilize this model of mud volcano evolution has similarities with igneous and salt tectonic systems to reduce drilling and geologic uncertainty mud volcano system extent and impacts on a reservoir can be assessed on 3 d seismic data simon stewart received his ph d from the imperial college london in 1992 in 1992 2000 he was seismic interpreter at amerada hess in support of exploration and appraisal drilling in the north sea in 2000 he moved to bp and has since worked on structural geology and well planning in the americas middle east and the former soviet union his special interest is in the integration of structural geology and seismic interpretation richard davies received his ph d from the university of edinburgh in 1995 in 1995 2003 he was with mobil and exxonmobil working on field development and exploration the north sea the west of shetlands and the west niger delta deep water slope in 2003 2005 he was a senior lecturer in earth sciences at cardiff university united kingdom currently he is professor and director of cerees center for research into earth energy systems durham university united kingdom his special interest is in seismic scale expression of fluid migration and diagenesis

change in the aerodynamic roughness height by saltating grains experimental assessment test of theory and operational parameterization data from an experiment at owens lake provided an opportunity to verify the validity of raupach s formula that predicts the apparent roughness height at equilibrium with saltation during wind erosion episodes in addition to that verification a simplification of raupach s formula is presented which allows the computation of the wind friction velocity affected by saltating sand grains without the need to measure the threshold wind friction velocity and to do iterative calculations this method estimates the increase of the wind friction velocity u above the nonsaltating wind friction velocity caused by the saltating grains u 0 3 u ut 2 where u and ut are the wind speed and the threshold wind speed respectively at 10m

shear stress partitioning in sparsely vegetated desert canopies shear velocity ratios were derived for six neighbouring localities representing rangeland abandoned farmland and a playa in the semi arid region of the sonoran desert near surface and above canopy wind speeds mostly below saltation threshold were used to evaluate the partitioning of shear velocities and shear stresses between the plant canopy and the surface the technique utilized represents an alternative to the threshold shear velocity ratio rt approach of musick and gillette land degradation and rehabilitation 1990 2 87 94 and results demonstrate the need for partitioning over a range of wind speeds shear velocity ratios were variable over the playa and abandoned farmland while variance in near surface wind speeds was highest over shrub dominated sites the relationship between lateral cover lc and shear velocity r is comparable to previous findings utilizing rt although methodological differences result in mean shear velocity ratios less than shear velocity ratios derived for threshold conditions with respect to the model of raupach et al journal of geophysical research 1993 98 d2 3023 3029 this may be attributed to the difference between measured shear stresses and the average shear stress on the exposed surface at high lateral covers shear velocity ratios are lower than threshold shear velocity ratios due to increased wake interactions or decreased drag on the shrub elements at higher wind speeds

an equilibrium relationship for shear velocity and apparent roughness lenght in aeolian saltation abstract an equilibrium relationship between shear velocity and apparent surface roughness is established for aeolian saltation velocity profiles of wind over blowing sand were digitized from eleven published data sets the 106 profiles were analyzed to obtain estimates of shear velocity and apparent surface roughness lenghts these values were used to test charnock s relationship for suitability in aeolian environments the results indicate that z 0 0 0091 u 2 g modifying charnock s model to describe wind over an equilibrium saltation field yields z 0 2d 50 30 0 0252 u u t 2 g the latter result is used to demonstrate that the focal point concept proposed by bagnold stems from the increase in apparent roughness with increased shear velocity the results demonstrate an excellent example of threshold controlled equilibrium in dynamic systems

secondary airflow and sediment transport in the lee of a reversing dune lee side windspeed and sediment transport were measured over a small 1 2 m transverse ridge in the silver peak dunefield west central nevada usa using an intensive array of 25 cup anemometers and seven total flux traps during crest transverse and transporting flow conditions u0 3crest 8 4 m s 1 windspeed near the surface of the lee slope averaged half 48 per cent that of crest speeds dimensionless speeds in the separation zone ranged from 0 2 to 0 8 that of the outer flow u12 along the boundary of the separation cell windspeed increased by 10 per cent of the crest speed before separation equilibrium of upper and lower wake regions was not observed by the documented eight dune heights suggesting that wake recovery may not occur over closely spaced dunes sediment transport measured directly on both the lee slope and interdune surfaces averaged approximately 15 per cent of crest inputs this suggests that a significant amount c 70 95 per cent of sediment transported over the crest moved as fallout for this data set flux was approximately proportional to the cube of the near surface windspeed u0 3 and in general there was an order of magnitude difference between flux measured at the crest and that measured within the separation zone transport direction in the separation zone was acutely oblique to the incident direction owing to secondary flow deflection beyond the interdune transport direction progressed from oblique to crest transverse this indicates that an appreciable amount of sediment may move laterally along the lee slope and interdune corridor under crest transverse flows regarding the grain size and sorting properties of transported sediment there was no significant difference in mean grain size over the dune although in general particles were finer and more poorly sorted in the lee copyright 1999 john wiley sons ltd

kinky profiles effects of soil surface heating upon vertical dust concentration profiles in the channel country of western queensland australia 1 in rangelands unlike cultivated fields soil surface conditions and vegetation cover are far from uniform field measurements taken within rangeland environments show that the shape of vertical dust concentration profiles can vary significantly between wind erosion events regression fits used to analyze vertical dust concentration profiles are therefore better for some events than others such variability has usually been explained as experimental error or noise or as a result of the nonuniformity of surface conditions a computer simulation model dsism is used to examine this variability in terms of wind erosion processes analysis of these simulation results together with field observations shows that nonuniformity in surface conditions alone cannot explain variations observed in the vertical dust concentration profiles these same simulations suggest that much of the variability in vertical dust concentration profiles is the result of thermal heating of the soil surface

evaluation of aeolian sand transport equations using intertidal zone measurements saunton sands england sand transport rates were measured using a vertical sand trap along the intertidal zone of a beach in north devon england together with simultaneous monitoring of the wind speed on the beach and moisture levels in the surface layers of sand the results of 88 sand trap samples in a wide range of wind speeds showed that moisture levels up to 14 in the top 1 2 mm of the beach sand have no discernible effect on the transport rates transport rates measured from areas of the beach where the moisture was below this level are compared with the rates predicted by seven expressions based on theoretical and wind tunnel research together with the empirical results of other published research measured transport rates range from 0 0001 to 0 22 kg m 1 s 1 the results indicate that expressions based on a power relation between the wind speed and the transport rate and which include a threshold velocity term provide the best estimates of the observed transport rates

groundwater salinity as a control on development of eolian landscape an example from the white sands of new mexico abstract the white sands of southern new mexico form the largest field of gypsum dunes in the world the juxtaposition of several different types of dunes within the field has long been recognized and has generally been attributed to changes in the rate of sand transport across the dune field however steven fryberger fryberger s g 2003 geology of white sands national monument web page www2 nature nps gov geology parks whsa recently hypothesized however that a primary control is groundwater salinity the white sands dune field is underlain by saline waters fryberger proposed that parabolic dunes could form in topographic highs that accumulated a lens of fresher water derived from precipitation water with lower salinity allowed vegetation to grow and stabilized the sand except for the active noses of the parabolic dunes this study is a test of that hypothesis a study transect was established across the boundary between parabolic and barchan dunes groundwater and soil at six sites were sampled during december 2004 and march may and june of 2005 two sites were established in the parabolic field two in the barchans and two in the transition zone between them groundwater was found to be three times more saline in the barchan area conductivity and chloride decreased across the transition zone a gps topographic survey revealed two abrupt topographic steps one at the boundary between the barchans and the transition zone and a second at the edge of the parabolic field a second larger topographic step was found outside the study area defining a higher parabolic dune field these data indicate that fryberger s 2003 hypothesis is correct and groundwater is controlling the dune field morphology the dune field did not begin to form until the mid holocene 6500 years ago a compilation of dates shows that the parabolic dune field has probably been stable for the last 3500 years in contrast the barchan area has been recently deflated and exposed 2000 year old sediment near the surface

velocity profiles measured on the windward slope of a transverse dune velocity gradients measured on the windward slope of a transverse dune show that flow acceleration strongly affects the turbulence structure of wind wind profiles measured below a height of 1 6m are nonlogarithmic and the altered nature of velocity profiles varies over the windward slope of a dune these findings suggest that calculated values of shear velocity are largely dependent upon the height and location of wind speed measurements as well as the strength of the prevailing wind moreover if bagnold type transport equations are used to calculate rates of sand transport on a dune wind speeds must be measured within 0 2 m of the dune surface if wind speeds are measured above this height the resulting errors in calculated shear velocity will manifest themselves as errors in calculated rates of sand transport if rates of sand transport are derived from wind speeds measured above 0 2 m the calculated rates may underestimate sand transport on the windward face of a dune as a result of flow acceleration in contrast if a dune has a separate crest upwind of the brink the expansion and subsequent deceleration of flow downwind from the crest may result in an overestimation of sand transport

aeolian shear stress ratio measurements within mesquite dominated landscapes of the chihuahuan desert new mexico usa a field study was conducted to ascertain the amount of protection that mesquite dominated communities provide to the surface from wind erosion the dynamics of the locally accelerated evolution of a mesquite coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements although shear stress partition models exist that can describe this their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements this study combines the use of meteorological towers and surface shear stress measurements with irwin sensors to measure the partition of shear stress in situ the surface shear stress within preferentially aligned vegetation within coppice dune development exhibited highly skewed distributions while a more homogenous surface stress was recorded at a site with less developed coppice dunes above the vegetation the logarithmic velocity profile deduced roughness length based on 10 min averages exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned while the site with more homogenously distributed vegetation showed very little variation in the roughness length this distribution in roughness length within an area defines a distribution of a resolved shear stress partitioning model based on these measurements ultimately providing potential closure to a previously uncorrelated model parameter

structural controls on a carbon dioxide driven mud volcano field in the northern apennines pieve santo stefano italy relations with pre existing steep discontinuities and seismicity the strong release of carbon dioxide co2 rich fluids in the axial zone of the northern apennines near pieve santo stefano is analysed in relation to both structural controls and the microseismicity that followed the earthquake of 26 november 2001 some vents recorded a transition from gas dominated emission to post seismic mud extrusion the co seismic rupture of a portion of the nw trending alto tiberina fault which bounds the quaternary upper tiber basin presumably broke the hydraulic seal trapping overpressured co2 rich fluid compartments and released a fluid pressure pulse fault pattern analysis has revealed that venting localises along ne trending steep faults associated with the regional transverse arbia val marecchia line bounding the basin to the northwest it is proposed that the transverse faults have been acting as permeable pathways allowing the post seismic transport of overpressured fluids to the surface during which the mud was mobilised a hypothetical correlation is also established between failure mechanisms and the 2001 aftershocks results of mohr constructions indicate that frictional fault reactivation is a suitable mechanism for explaining the seismic events along the nw trending normal fault while hydraulic fracturing is the most suitable to describe the seismicity occurring along the transverse faults

the east java mud volcano 2006 to present an earthquake or drilling trigger abstract on may 29th 2006 a mud volcano later to be named lusi started to form in east java it is still active and has displaced 30 000 people the trigger mechanism for this the world s largest and best known active mud volcano is still the subject of debate trigger mechanisms considered here are a the may 27th 2006 yogyakarta earthquake b the drilling of the nearby banjar panji 1 gas exploration well 150 m away and c a combination of the earthquake and drilling operations we compare the distance and magnitude of the earthquake with the relationship between the distance and magnitude of historical earthquakes that have caused sediment liquefaction or triggered the eruption of mud volcanoes or caused other hydrological responses based on this comparison an earthquake trigger is not expected the static stress changes caused by the rupture of the fault that created the yogyakarta earthquake are a few tens of pascals much smaller than changes in stress caused by tides or variations in barometric pressure at least 22 earthquakes and possibly hundreds likely caused stronger ground shaking at the site of lusi in the past 30 years without causing an eruption the period immediately preceding the eruption was seismically quieter than average and thus there is no evidence that lusi was primed by previous earthquakes we thus rule out an earthquake only trigger the day before the eruption started may 28th 2006 as a result of pulling the drill bit and drill pipe out of the hole there was a significant influx of formation fluid and gas the monitored pressure after the influx in the drill pipe and annulus showed variations typical of the leakage of drilling fluid into the surrounding sedimentary rock strata furthermore we calculate that the pressure at a depth of 1091 m the shallowest depth without any protective steel casing exceeded a critical level after the influx occurred fractures formed due to the excess pressure allowing a fluid gas mud mix to flow to the surface with detailed data from the exploration well we can now identify the specific drilling induced phenomena that caused this man made disaster

physical and logistical considerations of using ultrasonic anemometers in aeolian sediment transport research abstract recently ultrasonic anemometers uas have become available for precise high frequency measurement of three dimensional velocity and turbulence properties except for a few wind tunnel and computational fluid dynamics cfd simulations advances in aeolian sediment transport and bedform research have been limited to field studies using instrumentation that is either incapable of measuring turbulence e g cup anemometers or unable to withstand sediment laden airflow e g hotfilms in contrast extensive progress has occurred in fluvial research where turbulence instrumentation has been available for some time this paper provides a pragmatic discussion on using uas in aeolian research recent advances using this technology are reviewed and key physical and logistical considerations for measuring airflow properties and near surface shear stress using uas over complex terrain are discussed physical considerations include limitations of applying boundary layer theory to flow over natural surfaces such as non logarithmic velocity profiles resulting from roughness and topographically induced effects and the inability of instrumentation to measure within the thin constant stress region these constraints hinder accurate shear velocity u shear stress and sand transport estimation uas allow measurement of turbulent reynolds stress rs that in theory should equal profile derived shear stress discrepancies often exist between these quantities however due to three dimensional spanwise flow components and rapid distortion effects i e unbalanced production and dissipation of turbulence common in flow over complex terrain while the rs approach yields information on turbulent contributions to near surface stress generation little evidence exists showing that rs is a better measure of forces responsible for sediment transport consequently predictive equations for sediment transport using rs do not exist there is also a need to identify the role of micro turbulent events e g burst sweep cycles and macro turbulent structures e g separation cells shear layers in aeolian dynamics in field settings to validate recent wind tunnel and cfd simulations a conundrum exists regarding whether velocity data should be rotated to correct for potential sensor misalignment effects in unsteady non uniform flow over complex terrain streamline angles vary spatially and temporally with height and location thus determination of and correction to true streamline coordinates is difficult caution should be exercised with correction methods that remove implicit vertical velocity trends as this may preclude detection of geomorphically important flow behaviour e g lift at a dune crest and may complicate interpretations of rs instruments should be aligned with the underlying surface and flow visualization should be used to adjust sensor measurement planes as close as possible to local streamlines logistical considerations include sensor design advantages and operational limitations data communication formats and field deployment strategies each can affect measurement accuracy and are easily overlooked sampling range frequency and period are also important as they limit the range of velocities and scales of turbulence that can be characterized ultrasonic anemometers offer a new sampling resolution to measure turbulent airflow properties in field settings with proper considerations of their limitations uas may allow researchers to close the gap between fluvial research and develop more robust models of aeolian processes and morphodynamics

methodology for reconstructing wind direction wind speed and duration of wind events from aeolian cross strata 1 a methodology for reconstructing wind direction speed and event duration from aeolian dune cross strata was developed from analysis of crescentic dunes at white sands new mexico during wind events dune lee faces were surveyed lee face deposits mapped deposition rates measured grain size sampled by stratification type and winds characterized from meteorological and field data the spatial distribution of lee face stratification styles is a function of the incidence angle formed between the wind and the brinkline with secondary controls by wind speed and dune sinuosity and height sets of wind ripple strata form at incidence angles of 25 40 grainfall grainflow foresets over wind ripple bottomsets at 40 70 and grainflow grainfall foresets at 70 90 erosional reactivation surfaces form at incidence angles up to 15 bypass surfaces up to 25 the total sediment load is fractionated within lee face stratification types wind speed can be reconstructed from relationships between grain size transport mode shear velocity and grain settling velocity where the full range of grain transport modes occurs and grain size is limited by shear stress the shear velocity and grain size range in each transport mode can be estimated by assuming the coarse fraction in grainflow strata traveled in creep and the coarse fraction in grainfall traveled in saltation the minimum duration of a wind event can be estimated using measures of shear velocity dune height and dune forward migration method limitations arise with source area control on grain size extremes in wind events and severe truncation of sets of cross strata

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

mean airflow patterns upwind of topographic obstacles and their implications for the formation of echo dunes a wind tunnel simulation of the effects of windward slope 1 secondary airflow plays an important role in dune formation and development in the case of the echo dunes that form upwind of an obstacle it introduces considerable complexity because both the initiation and development processes are influenced by airflow patterns in this study we measured the variations of airflow in front of obstacles with different windward stoss slope angles by means of particle image velocimetry in a series of wind tunnel tests the windward slope angle was the key factor in determining the secondary airflow patterns the horizontal velocities decreased and the vertical velocities increased as the airflow approached perpendicular to the obstacle and a vortex of reversed flow formed in front of obstacles with a stoss slope of 60 or steeper the positions of airflow separation and of the core of the reversed vortex were a function of the windward slope angle depending on the position of the reverse vortex and its significance for the formation of echo dunes the windward slope could be divided into three groups 65 or less 70 75 and 80 or more the horizontal velocity profiles deviated from a log linear distribution resulting in five airflow regions with different rates of change of horizontal velocity we discuss the significance of these velocity variations for sand accumulation and the effects of each airflow region on echo dune formation

the three dimensional shear wave structure in the mantle by overtone waveform inversion i radial seismogram inversion summary the three dimensional 3 d shear wave structure of the mantle down to the depth of about 900 km is obtained by inverting waveforms of radial component seismograms radial component seismograms contain large amplitude overtone signals which circle the earth as wave packets and are sometimes called x1 x2 x3 we use data which contain r1 x1 and x2 and filtered between 2 and 10mhz it is shown that unless each seismogram is weighted all seismograms are not fitted uniformly only data from large earthquakes are fitted and the final velocity anomalies are biased by the small number of large earthquake data resolution is good at shallow depths becomes worse in the intermediate depth range between about 400 and 500 km and then becomes better at greater depth ranges 600 900km even though we use only spheroidal mode data velocity anomalies in the shallow structure show excellent correlation with the age of the surface rocks of the earth in the deeper regions between about 600 and 900km south america shows a fast velocity anomaly which may indicate the slab penetration beyond 700 km there another region which shows a fast velocity anomaly is the mariana trench but other subduction regions do not show such features

reply to comment by c collettini on structural controls on a carbon dioxide driven mud volcano field in the northern apennines pieve santo stefano italy relations with pre existing steep discontinuities and seismicity

aspherical heterogeneity of the mantle from phase velocities of mantle waves long period surface waves are used to map the lateral heterogeneity of the upper 100 600 km of the mantle there is good correlation of velocity with surface tectonics and heat flow convergence regions are generally slow for love waves and fast for rayleigh waves back arc basins have slower than average shallow mantle some island arcs show evidence of fast material at greater depth deep seated slow anomalies underlie the red sea afar region of north east africa western north american northern east pacific rise indian ocean triple junction and the tasman sea campbell plateau regions the fastest regions are in the north central australia new guinea and the south atlantic