coastal dunefields of south brazil as a record of climatic changes in the south american monsoon system abstract southern brazil coastal dunefields are undergoing a stabilization process that appears to be influenced by climate change although this process is relatively well known in the literature the precise climatic mechanisms involved were not fully understood until now here we propose a new method for integrating meteorological data with dunefield morphology analyses by remote sensing to better understand the impacts of recent climate change on dunefield dynamics based on this approach three successive morphological phases were identified for the santa catarina central coast dunefields since 1938 i increased sand saturation ii reduced sand saturation with consequent accelerated dune migration and iii decelerated dune migration with trends of stabilization by the vegetation cover for the coastal dunefields of southern brazil the stabilization process can be explained mechanistically by an increase in precipitation and decrease of wind power both of which were correlated with the intensification of the south american monsoon system

biodegradation of tar sand bitumens from the ardmore anadarko basins oklahoma ii correlation of oils tar sands and source rocks abstract in an earlier paper we reported the effects of biodegradation on tar sand bitumens from the southern part of the ardmore and anadarko basins in this paper we wish to describe geochemical correlations that have been made between the tar sand bitumens and oils produced from various formations in the pauls valley area 25 miles to the north it was determined that the tar sands were formed from a source similar to many of these oils whose reservoir ages ranged from ordovician to pennsylvanian the oils had been previously divided into two major groups on the basis of their biomarker distributions with one group 80 of the oils studied proposed to have been sourced from the woodford shale devonian and the other group from the viola limestone ordovician the tar sand bitumen oil correlation study based on hydrocarbon and porphyrin biomarker distributions and pyrolysis gas chromatography of asphaltenes has shown that the tar sand bitumen appears to be genetically related to the group of oils derived from the woodford shale and more specifically to those present in the oil creek formation ordovician of the anadarko basin

aeolian sand drift from the intertidal zone on a temperate beach potential and actual rates this paper compares the amount of sand that is potentially moved into a coastal dune system from a beach using estimates based solely on the wind force with actual measured amounts the actual sand inputs are determined by measuring sand level changes each month over a period of eighteen months along a 1760 m section of foredune on braunton burrows southwest england the calculation procedure used to estimate the potential rates of sand drift is based on the capacity of the wind force to transport sand using a published transport equation white 1979 the results show that the actual movement rates are markedly smaller than the potential rates for all months except in the summer meteorological variables and the watertable level in the adjacent dune system are used in an empirically derived regression equation in an attempt to explain the large discrepancy between the potential and actual movement rates the resulting corrected potential movement rates are a closer estimate to the actual rates but there remains much unexplained variance

flexural ridges trenches and outer rises around coronae on venus high resolution altimetry collected by the magellan spacecraft reveals trench and outer rise topographic signatures around major coronae e g eithinoha heng o artemis and latona in addition magellan synthetic aperature radar images show circumferential fractures in areas where the plates are curved downward both observations suggest that the lithosphere around coronae is flexed downward by the weight of the overriding coronal rim or by the negative buoyancy of subducted lithosphere we have modelled the trench and outer rise topography as a thin elastic plate subjected to a line load and bending moment beneath the corona rim the approach was tested at northern freyja montes where the best fit elastic thickness is 18 km in agreement with previously published results the elastic thicknesses determined by modelling numerous profiles at eithinoha heng o artemis and latona are 15 40 37 and 35 km respectively at eithinoha artemis and latona where the plates appear to be yielding the maximum bending moments and elastic thicknesses are similar to those found at the middle america mariana and aleutian trenches on earth respectively estimates of effective elastic thickness and plate curvature are used with a yield strength envelope model of the lithosphere to estimate lithospheric temperature gradients at heng o artemis and latona temperature gradients are less than 10 k km which correspond to conductive heat losses of less than one half the expected average planetary value we propose two scenarios for the creation of the ridge trench and outer rise topography differential thermal subsidence and lithospheric subduction the topography of heng o is well matched by the differential thermal subsidence model however at artemis and latona the amplitudes of the trench and outer rise signatures are a factor of 5 too large to be explained by thermal subsidence alone in these cases we favor the lithospheric subduction model wherein the lithosphere outboard of the corona perimeter subducts rolls back and the corona diameter increases

wind tunnel experiments on vertical distribution of wind blown sand flux and change of the quantity of sand erosion and deposition above gravel beds under different sand supplies wind tunnel experiments were carried out with respect to the vertical distributions of wind blown sand flux and the processes of aeolian erosion and deposition under different wind velocities and sand supplies above beds with different gravel coverage preliminary results revealed that the vertical distribution of wind blown sand flux was a way to determine whether the gobi sand stream was the saturated one or not it had different significances to indicate characteristics of transport and deposition above gobi beds whether bed processes are of aeolian erosion or deposition was determined by the sand stream near the surface especially within 0 6 cm height while the sand transport was mainly influenced by the sand stream in the saltating layer above the height of 6 cm the degree of the abundance of sand supply was one of the important factors to determine the saturation level of sand stream which influenced the characteristic of aeolian erosion and deposition on gravel beds given the similar wind condition the sand transport rates controlled by the saturated flow were between 2 and 8 times of the unsaturated one those bed processes controlled by the saturated flow were mainly of deposition and the amount of sand accumulation increased largely as the wind speed increased in contrast the bed processes controlled by the unsaturated flow were mainly of aeolian erosion meanwhile there was an obvious blocking sand ability within the height of 0 2 cm and the maximal value of sand transport occurred within the surface of 2 5 cm height

aeolian sand strip mobility and protodune development on a drying beach examining surface moisture and surface roughness patterns measured by terrestrial laser scanning ephemeral aeolian sand strips are commonplace on beaches their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns however due to their temporary nature little is known of their formation mobility or the specifics of their interaction with beach surface characteristics similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well their resolution over mainly dry sand close to the aeolian transport threshold is not ideal particularly where moisture gradients close to the surface are large in this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development surface roughness and surface moisture our results demonstrate that as the beach surface dries sand transport increases with sediment erosion occurring at the wet dry surface boundary and deposition further downwind this dynamic structure dependent upon changing surface moisture characteristics results in the formation of a rippled sand strip and ultimately a protodune our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings the terrestrial laser scanner provides a suitable apparatus with which to accomplish this

theoretical and measured aeolian sand transport on a barrier island louisiana usa over the past 100 years the isles dernieres a low lying barrier island chain along the coast of central louisiana usa has undergone more than 1 km of northward beach face retreat with the loss of 70 of its surface area the erosion results from a long term relative sea level rise coupled with day to day wind and wave action that ultimately favours erosion over deposition at a site in the central isles dernieres 8 days of wind and beach profile measurements during the passage of one winter cold front documented aeolian erosion and deposition patterns under both onshore and offshore winds for offshore winds the theoretical erosion rate based on wind shear velocity closely matched the measured erosion rate for onshore winds the theoretical rate matched the measured rate only after being corrected by a factor that accounted for beach face morphology in late february 1989 a strong cold front moved into coastal louisiana that cold front stalled over the gulf of mexico resulting in 4 days of strong northerly winds at a study site on the isles dernieres during those 4 days the wind moved sand from the backshore to the upper beach face when the cold front finally moved out of the area the wind shifted to the south and decreased in strength the onshore wind then restored some of the upper beach face sand to the backshore while increased wave activity moved the rest into the nearshore the theoretical estimate of 1 28 m3 m 1 for the rate of sand transport by the northerly wind compares well with the measured backshore erosion rate of 1 26 m3 m 1 which was determined by comparing beach profiles from the start and end of the period of northerly winds the theoretical estimate of 0 04 m3 m 1 for the rate of sand transport by the southerly wind however is notably less than the measured rate of 0 45 m3 m 1 the large discrepancy between the two rates can be explained by a difference in the shear velocity of the wind between the beach face where the erosion occurred and the backshore where the wind stress was measured using an empirical relationship for the wind shear drag coefficient as a function of coastal environment the theoretical estimate for the rate of sand transport by the southerly wind becomes 0 44 m3 m 1

airflow up the stoss slope of sand dunes limitations of current understanding the windward stoss side of a sand dune acts as a streamlined obstacle in the path of the wind continuity principles necessitate compression of the flow field up the stoss slope of a dune and shear stress must progressively increase as the flow accelerates measurements in transverse flow over thirteen dunes at padre island texas the algodones california and white sands new mexico confirm that velocity profiles on the stoss slope are not log linear and that flow acceleration occurs very close to the surface within an internal boundary layer as a consequence in the overlying flow where measurements have historically been made an overall decrease in shear stress occurs up the slope the actual shape of the velocity profiles and the identification of the appropriate segment of the profile from which to derive the shear stress that drives saltation represent major problems not approachable by traditional means

effects of time dependent moisture content of surface sediments on aeolian transport rates across a beach wildwood new jersey u s a a one day field investigation on an unvegetated backbeach documents the importance of surface sediment drying to aeolian transport surface sediments were well sorted fine sand moisture content of samples taken in the moist areas on the backbeach varied from 2 9 to 9 2 per cent lack of dry sediment inhibited transport prior to 08 50 by 09 10 conspicuous streamers of dry sand moved across the moist surface barchan shaped bedforms 30 to 40 mm high and composed of dry sand moisture content 0 10 per cent formed where sand streamers converged the surface composed of dry sand increased from 5 per cent of the area of the backbeach at 09 50 to 90 per cent by 12 50 mean wind speeds were beetween 5 6 and 8 6 m s 1 at 6 m above the backbeach corresponding shear velocities were always above the entrainment threshold for dry sand and below the threshold for the moist sand on the backbeach measured rates of sand trapped by vertical cylindrical traps increased during the day relative to calculated rates the measured rate of sand trapped on the moist foreshore was higher than the rate trapped on the backbeach during the same interval indicating that the moist foreshore moisture content 18 per cent was an efficient transport surface for sediment delivered from the dry portion of the beach upwind measured rates of sand trapped show no clear relationship to shear velocities unless time dependent surface moisture content is considered results document conditions that describe transport across moist surfaces in terms of four stages including 1 entrainment of moist sediment from a moist surface 2 in situ drying of surface grains from a moist surface followed by transport across the surface 3 entrainment and transport of dry sediment from bedforms that have accumulated on the moist surface and 4 entrainment of sand from a dry upwind source and transport across a moist downwind surface 1997 john wiley sons ltd

coronae on venus morphology classification and distribution abstract two major types of circular features with no direct morphologic analog on the terrestrial planets were identified in venera 15 16 radar images of venus coronae and corona like features coronae are irregular to circular structures characterized by a complex interior zone and maximum widths of 170 690 km corona like features resemble coronae but lack an annulus of ridges twenty one structures that fit the definition of coronae have been identified in venera 15 16 coverage along with eleven corona like features each group has been subdivided into three classes based on general morphology symmetrical coronae are characterized by circular to oval form with interiors characterized by flows domes and tectonic ridges asymmetrical coronae have similar morphology but have only a partial annulus or are asymmetrical about a central axis subdued coronae are dominated by smooth plains with flooded and embayed annuli double corona like structures are composed of two linked rings and are found along ridge belts in the region east of atalanta planitia irregular corona like features are surrounded by a rim rather than an annulus as are the double structures and are very subdued in appearance heart shaped corona like features are rounded at one end and form a wedge at the other end we interpret the classes of coronae and corona like features to have a similar mode of origin with differences in morphology due to the stage of evolution and or varying amounts and significance of geologic processes i e tectonism volcanism gravitational relaxation that occur during their evolution corona evolution is characterized by early uplift and volcanism followed by annulus formation formation of a peripheral trough may occur in the middle to late stages of corona evolution followed by extensive volcanism and lowering of topographic relief both coronae and corona like features are interpreted to have formed as a result of uplift and volcanism caused by a thermal anomaly at depth followed by gravitational relaxation

temporal and spatial variabilities in the surface moisture content of a fine grained beach abstract this study examined spatial and temporal variations in the surface moisture content of a fine grained beach at padre island texas usa surface moisture measurements were collected on a 27 24 m grid that extended from the dune toe to the upper foreshore the grid was surveyed at 2 to 4 h intervals for two tidal cycles generating 17 maps of the spatial distribution of surface moisture simultaneous measurements of air temperature and humidity wind speed and direction tidal elevation and water table elevation were used to interpret observed changes in surface moisture it was found that the spatial distribution of surface moisture was broadly characterized by a cross shore gradient of high to low content moving landward from the swash zone the distribution of surface moisture was conceptualized in terms of three zones saturated 25 intermediate or transitional 5 25 and dry

predicting aeolian sand transport revisiting the white model the derivation and history of the frequently cited aeolian transport model of white are considered in light of the continued replication of an error in the original expression the error may have escaped notice because the expression is still dimensionally correct and it yields predictions that appear reasonable in comparison with both the predictions of other models with field data the incorrect expression has come to be identified as a distinct model however the correct formulation of the white model is in fact a rearrangement of the kawamura model with a slightly smaller c 6 empirical coefficient 1997 john wiley sons ltd

the dynamic effects of moisture on the entrainment and transport of sand by wind abstract there is an increasing awareness of the influence of surface moisture on aeolian entrainment and transport of sediment existing wind tunnel studies have shown the impact of a limited range of moisture contents on entrainment thresholds but similar investigations are lacking in the field the research reported here investigated the influence of changes in surface moisture content on sand entrainment and transport on a meso tidal beach in anglesey north wales high frequency 1 hz wind velocities measured with hot wire anemometers were combined with grain impact data from a sensit monitor and mass flux measurements from a standard sand trap surface and near surface moisture contents were assessed gravimetrically from surface sand scrapes and also directly by using a thetaprobe critical threshold values for entrainment were specified using a modified form of the time fraction equivalence method stout j e zobeck t m 1996a establishing the threshold condition for soil movement in wind eroding fields proceedings of the international conference on air pollution from agricultural operations mwps c 3 kansas city 7 9 february 1996 pp 65 71 results indicate a time dependent change in dominant control of the sand transport system from moisture to wind speed dependent upon the moisture content of the surface sediment this interchange between controlling parameters on both entrainment and transport was very sensitive to prevailing moisture conditions and took place over a period of minutes to hours under conditions experienced in the experiments presented here the critical moisture threshold for sediment entrainment was determined to be between 4 and 6 higher than the 1 4 specified in previous wind tunnel experiments furthermore a moisture content of nearly 2 where moisture was adhered to transported sediment appeared to have little or no impact on the rate of sand flux

global distribution and characteristics of coronae and related features on venus implications for origin and relation to mantle processes coronae on venus range from 60 to over 2000 km across and are characterized by a complex range of morphologies the annuli around coronae range from about 10 to 150 km across and have tectonic features ranging from extensional to compressional to a combination of both topographically coronae are domes plateaus plateaus with interior lows and rimmed depressions a subset of features classified here as coronae corresponds to depressions and is interpreted to consist of large scale calderas a number of features have been identified with many of the basic characteristics of coronae similar interior deformation associations with volcanism high topography but lacking a distinct tectonic annulus these features tend to be somewhat smaller than coronae and may represent failed coronae or coronae in an early stage of evolution the size distribution of coronae and coronalike features with maximum widths greater than about 250 km is well represented by a power law of the form n d kd where n is the number of coronae with maximum widths greater than d km and 3 05 the spatial distribution of coronae is not random the features are concentrated in a few groups and along several chains coronae are similar in many morphologic characteristics to major volcanic shield structures and volcanic rises such as western eistla regio the largest corona artemis is actually larger than several volcanic rises on venus coronae and volcanic rises appear to be surface manifestations of mantle plumes there is no evidence of any systematic variation in age along chains of coronae as occurs in hotspot chains on earth instead a number of multiple and overlapping coronae may indicate limited movement of the surface above a hotspot or mantle plume the morphology and size distribution of coronae highlands and major shields suggest that mantle upwelling on venus operates either on several spatial scales with coronae representing smaller scale upflows and major volcanic rises representing larger convective upwellings or on several temporal scales with coronae representing shorter duration upflows and major volcanic rises representing long term upwellings

on the modelling of two dimensional aeolian dunes in this study the modelling of aeolian dunes is treated from the background of the physical processes that form them the paper concentrates on two dimensional modelling which can be applied to transverse and barchan dunes the basic assumptions and equations are discussed and three models are presented a a kinematic model which is based on a linear variation of the sediment transport with the topographic height b an analytical model based on a boundary layer model of the wind velocity and bagnold s linearized sediment transport formula c a generalization of this analytical model in a computer program which includes a simple routine for simulating the redistribution of sediment through avalanching the relative importance of the simplifications is considered and indications are given for the practical applications of these three models in field studies

corona structures on venus models of origin coronae on venus are circular to elongate structures with maximum widths of 150 1000 km characterized by annuli of concentric ridges surrounding complex interiors the features have raised topography relative to the surroundings they are associated with volcanic activity and most are partially surrounded by a peripheral trough variations in morphology between individual coronae are due to differences in their stage of evolution and or differences in the relative significance of the geologic processes that occur in each stage we examine models for three processes that may be involved in corona origin and evolution 1 a hotspot or rising mantle diapir model 2 a sinking mantle diapir model and 3 gravitational relaxation of topography rising mantle diapirs are caused by heating at depth e g hotspot while sinking mantle diapirs may result from cooling or a phase change causing increased density and negative buoyancy at the base of the lithosphere the hotspot model is most consistent with the major characteristics of coronae with gravitational relaxation occurring as a modificational process the sinking mantle diapir would produce dominant central compression that has not been observed at coronae however higher resolution image and altimetry data from magellan can be used to distinguish more fully between the two models coronae in various states of formation and degradation can be identified in the venera 15 16 data suggesting that the process may be continuing today

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

grains in motion a review abstract this review paper aims to present a practical integrated procedure for the prediction of sediment transport rates in both the continental and marine environment based on the settling velocity of particles such studies have important applications in diverse fields such as civil and coastal engineering sedimentology and environmental geology where they can assist in flood control and the prevention of contaminant dispersal by wind and water as well as the siltation of dams and harbours the formation of placer deposits including gold diamonds and other heavy minerals is also controlled by sediment transport processes so that these studies can form the basis for more efficient exploration programs the first part of the paper discusses some basic principles important in sediment transport followed by an overview of published methods to determine the settling velocity of differently shaped particles including natural grains the application of settling velocity to predict the entrainment threshold of sediments on plane horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed which finally leads to the determination of sediment transport rates over plane and rippled beds the validity of this approach to natural conditions is tested against published field data where possible other widely used methods are also critically discussed pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments

coronae of mnemosyne regio morphology and origin abstract coronae are circular to elliptical structures 150 600 km across characterized in venera 15 16 and arecibo radar images by an annulus of concentric ridges the interiors of the structures are geologically complex displaying volcanic flows domes and radial concentric and or obliquely trending ridges and are generally distinct from the exterior the mnemosyne regio area to the west of ishtar terra contains seven coronae the largest cluster of coronae identified on venus on the basis of the morphologic and topographic characteristics of the coronae in the mnemosyne region we assess several possible models of corona origin using cross cutting and stratigraphic relationships we have been able to identify a sequence of features and events for this group of coronae and have determined that a variety of processes contribute to the origin and evolution of coronae we find that several processes associated with diapirism or hotspots and gravitational relaxation of high topography are most consistent with observed corona topography and morphology and are thus likely to have been significant in the formation and evolution of coronae on the basis of these observations and stratigraphic relationships the following sequence of events is outlined for the formation and evolution of coronae in this region 1 regional volcanic and tectonic activity 2 localized uplift and volcanism caused by diapirism or hotspots 3 annulus and trough formation related to gravitational relaxation accompanied by further volcanic activity 4 continued local volcanic flooding of the corona annulus and trough differences in morphology between coronae reflect variations in amount and significance of these geologic processes coronae in other regions exhibit the same overall characteristics as the mnemosyne coronae and support a similar origin for the majority of coronae

understanding wind blown sand six vexations abstract the study of aeolian geomorphological systems over the last half century has advanced along several important fronts supported by developments in technologies and analytic methods and the evolution of modeling approaches remote sensing has led to a wealth of knowledge concerning the distribution and dynamics of dunes on earth and elsewhere and wind tunnels have elucidated the roles of aeolian processes in reshaping surfaces improvements in laboratory and field instrumentation allow measurement of aeolian sand transport systems at levels of detail unimaginable when the binghamton geomorphology symposium began we have seen for example the advent of large sophisticated field campaigns and advanced modeling approaches using cellular automata and computational fluid dynamics methods select avenues of development especially concerned with depositional environments are briefly summarized advances in many fields have not been matched with proportional advances in our ability to predict rates of sand transport in natural environments one of the most fundamental challenges at least eight commonly cited sand transport rate models do not agree with each other and do not replicate field observations even under near ideal conditions this review focuses on select reasons why that might be so and categorizes those reasons into six principal theoretical and empirical vexations that have made sand transport an intractable problem predicting rates of transport characterizing grain size characterizing fluid and sand densities estimating shear velocity predicting the threshold of motion including the effects of sand moisture content and understanding granular electrification the examination of potential sources of error in the rate of transport and threshold of motion models leads to a point by point consideration of our current assumptions and protocols or lack thereof the objective is to help us identify the hard targets and the soft targets for future research

aeolian sand transport at the lanphere dunes northern california aeolian sand transport was studied at the lanphere dunes a coastal dune complex in northern california by comparing slipface advance rates with transport predicted based on local wind data the slipfaces of a 2 5 m high transverse ridge and 10 m high parabolic dune were monitored over a period of three months to estimate sand discharge the study was performed during the dry season which has the maximum sand driving potential over the three month study period average sand discharge was 12 5 m3 per m width per year at the transverse ridge and 8 8 m3 per m width per year at the parabolic dune a method was developed for modelling slipfaces that are sinuous and where sediment transport rates are not constant across the width of the slipface field measurements were used to generate three dimensional representations of dune slipfaces periodic measurements over the course of three months were used to compute the volume of displaced sediment theoretical sand transport was computed from local wind data using the bagnold model and compared with the observed transport rates predicted rates were substantially lower than observed rates wind velocities rarely exceeded the threshold velocity discrepancies between the observed and predicted values appear to be caused by a combination of wind data recording procedures and differences between wind velocities at the anemometer location and the site where sand transport was measured wind data collected by weather bureaux have been utilized in numerous studies for modelling sediment transport such data typically have sample intervals of one hour or greater and are often averaged prior to reporting the effect of averaging was investigated by comparing sand transport estimates based on daily average wind velocities with those based on the original hourly observations the daily average data were depleted of high velocity winds and sand transport estimates were accordingly much lower than those based on the hourly data copyright 2000 john wiley sons ltd

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

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

the geology and geomorphology of the venus surface as revealed by the radar images obtained by veneras 15 and 16 a region by region condensed description of almost all of the area that was radar photographed by veneras 15 and 16 is presented using some generalizations the diversity of terrain was reduced to a discrete set from which a geological morphological map was constructed the predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types ridge and band patchy rolling plain dome and butte plain smooth plain and high smooth plain stratigraphically the ridge and band plains are the oldest and the smooth plains are the youngest the stratigraphic position of the other types is yet to be determined large sections of the plains show similarities to the mare type basaltic plains of the moon mercury and mars other types of terrain are combinations of ridges and grooves in various patterns linear parallel orthogonal diagonal or chevron like and chaotic in some places the ridge and groove terrain is stratigraphically below the plain material but in other places it appears to be plain material that has been subsequently deformed near the eastern and western boundaries of ishtar terra large several hundred kilometers in diameter ring like features can be seen that are named coronae or ovoids evidence of tectonic deformation and the presence of flow like patterns support their designation as volcano tectonic features beta regio seems to be an uplifted plain showing evidence of rifting and volcanism all types of terrain are sparesely peppered with craters of obvious impact morphology their average density gives the plain an age range of 0 5 to 1 109 years the fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking at least for the last 0 5 to 1 109 years no evidence for water erosion sedimentation processes has been found the tectonic activity of venus has no equivalent on the moon mercury or even mars and can be compared only with that of the earth intensive horizontal deformation previously known only on earth occurs on venus but in a characteristic venusian style

a parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment abstract a new parameterisation for the threshold shear velocity to initiate deflation of dry and wet particles is presented it is based on the balance of moments acting on particles at the instant of particle motion the model hence includes a term for the aerodynamic forces including the drag force the lift force and the aerodynamic moment force and a term for the interparticle forces the effect of gravitation is incorporated in both terms rather than using an implicit function for the effect of the aerodynamic forces as reported earlier in literature a constant aerodynamic coefficient was introduced from consideration of the van der waals force between two particles it was further shown that the effect of the interparticle cohesion force between two dry particles on the deflation threshold should be inversely proportional to the particle diameter squared the interparticle force was further extended to include wet bonding forces the latter were considered as the sum of capillary forces and adhesive forces a model that expresses the capillary force as a function of particle diameter squared and the inverse of capillary potential was deduced from consideration of the well known model of fisher and the young laplace equation the adhesive force was assumed to be equal to tensile strength and a function which is proportional to particle diameter squared and the inverse of the potential due to adhesive forces was derived by combining the capillary force model and the adhesive force model the interparticle force due to wet bonding was simplified and written as a function of particle diameter squared and the inverse of matric potential the latter was loglinearly related to the gravimetric moisture content a relationship that is valid in the low moisture content range that is important in the light of deflation of sediment by wind by introducing a correction to force the relationship to converge to zero moisture content at oven dryness the matric potential moisture content relationship contained only one unknown model parameter viz moisture content at 1 5 mpa working out the model led to a rather simple parameterisation containing only three coefficients two parameters were incorporated in the term that applies to dry sediment and were determined by using experimental data as reported by iversen and white sedimentology 29 1982 111 the third parameter for the wet sediment part of the model was determined from wind tunnel experiments on prewetted sand and sandy loam aggregates the model was validated using data from wind tunnel experiments on the same but dry sediment and on data obtained from simulations with the model of chepil soil sci soc am proc 20 1956 288 the experiments showed that soil aggregates should be treated as individual particles with a density equal to their bulk density furthermore it was shown that the surface had to dry to a moisture content of about 75 of the moisture content at 1 5 mpa before deflation became sustained the threshold shear velocities simulated with our model were found to be in good agreement with own observations and with simulations using chepil s model

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

wind blown sand on beaches an evaluation of models five models for predicting rates of aeolian sand transport were evaluated using empirical data obtained from field experiments conducted in april 1994 at a beach on inch spit co kerry republic of ireland measurements were made of vertical wind profiles to derive shear velocity estimates beach slope and rates of sand transport sediment samples were taken to assess characteristics of grain size and surface moisture content estimates of threshold shear velocity were derived using grain size data after parsing the field data on the basis of the quality of shear velocity estimation and the occurrence of blowing sand 51 data sets describing rates of sand transport and environmental conditions were retained mean grain diameter was 0 17 mm surface slopes ranged from 0 02 on the foreshore to about 0 11 near the dune toe mean shear velocities ranged from 0 23 m s 1 just above the observed transport threshold to 0 65 m s 1 rates of transport ranged from 0 02 kg m 1 h 1 to more than 80 kg m 1 h 1 these data were used as input to the models of bagnold bagnold r a 1936 the movement of desert sand proc r soc london a157 594 620 kawamura kawamura r 1951 study of sand movement by wind translated 1965 as university of california hydraulics engineering laboratory report hel 2 8 berkeley zingg zingg a w 1953 wind tunnel studies of the movement of sedimentary material proc 5th hydraulics conf bull 34 iowa city inst of hydraulics pp 111 135 kadib kadib a a 1965 a function for sand movement by wind university of california hydraulics engineering laboratory report hel 2 8 berkeley and lettau and lettau lettau k and lettau h 1977 experimental and micrometeorological field studies of dune migration in k lettau and h lettau eds exploring the world s driest climate university of wisconsin madison ies report 101 pp 110 147 correction factors to adjust predictions of the rate of transport to account for the effects of slope and moisture content were calculated using the models of bagnold bagnold r a 1973 the nature of saltation and bed load transport in water proc r soc london ser a 332 473 504 and belly belly p y 1964 sand movement by wind u s army corps eng cerc tech mem 1 washington d c 38 pp respectively none of the models was able to produce a strong correspondence between measured and predicted rates of transport best results were obtained using the bagnold and zingg models and the kadib model was the least viable of this group the influence of sediment moisture content appeared to be the critical factor in degrading model viability overall none of the models is adequate for general applications to coastal aeolian environments where moisture content complications tend to override the predictive competence of the simple transport formulations c 1998 elsevier science b v

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

field measurement and numerical modelling of aeolian mass flux distributions on a sandy beach the vertical and horizontal distributions of aeolian mass flux were measured at oceano dunes california and these data were used to evaluate a numerical model of saltation grain size analyses showed that the distributions of the modal sediment size class corresponded closely to those of the total sediment population and modelling thus focused on replicating the distributions of the mean grain size although much previous work has assumed that the mean launch speed of saltating particles varies in proportion to shear velocity simulations using a constant mean launch speed were found to yield the closest approximations to the mass flux distributions observed in the field both exponential and gamma distributions of launch velocity produced realistic simulations although the latter approach required the inclusion of an additional reptation component to achieve good results a range of mean launch angles and an equivalent sphere correction were also found to generate comparable results providing the other input parameters could be varied freely all the modelling approaches overestimated the proportion of mass flux occurring at the bottom of the vertical distributions and underestimated the proportion occurring at the upwind end of the horizontal distributions no theoretical shortcoming that would account for these small but systematic discrepancies could be identified and experimental error thus represents a more plausible explanation the conclusion that mean grain launch speeds are essentially constant and independent of shear velocity suggests that the additional kinetic energy extracted by grains under more energetic wind conditions is largely transferred to the bed and that increases in the transport rate are therefore driven primarily by the ejection of additional grains it is suggested that the kinetic energy of rebounding grains is constrained by the ability of the bed to resist deformation equivalent to a plastic limit hence grains of larger mass diameter rebound from the bed at lower speeds and follow shorter lower trajectories as has been widely observed previously

aeolus ii an interactive program for the simulation of aeolian sedimentation abstract a computer program has been developed to simulate two or three dimensional topographic change associated with aeolian sediment transport because predictions generated by available models of aeolian transport can vary by about an order of magnitude for a given set of environmental conditions selection of an appropriate model is problematic this program includes a number of models and provides for interactive selection of a desired model combination s to allow for comparison between model predictions topography represented by a set of coordinates in two or three dimensions is defined by bins of sediment differential rates of transport between adjacent bins resulting from variations in grain size slope and surface moisture content are used to determine mass flux and to adjust the topography in an iterative fashion sub routines allow the simulation of temporally varying levels of surface moisture resulting from evaporation and periodic restoration of upwind boundary conditions the wind field can be represented by a constant shear velocity by a spatial cross shore distribution of shear velocities or by a time series of values representing multiple wind events output is in the form of a graphic display or tabulated results written to disk example results are presented which qualitatively suggest that simulated topographic changes are reasonable areas where further refinement is needed to improve correspondence with reality are identified and discussed

porphyrin distributions in crude oils from the jianghan and biyang basins china abstract a number of oils tar sands and extracts of suspected source rocks from the jianghan and biyang basins of china have been studied to investigate their porphyrin content the results obtained suggest that these distributions are controlled to a large extent by the nature of the depositional environment and the maturity levels of the sediments it is proposed that the predominance of ni porphyrins in the sediments of these basins is caused mainly by the high ni content of the groundwater the relatively high content of a c32 porphyrin isomer with a five membered ring with a methyl substituent is indicative of environments with very high salinity the porphyrin distributions have been affected through thermal maturation with the major changes being dealkylation alkylation within etio porphyrins the instability of ni dpep porphyrins is suggested as a major reason for the rarity of dpep porphyrins in chinese oils the ratios of dpep etio or dpep etio dpep c 31 etio a c 28 etio b and etio a c 31 c 30 are useful as thermal maturity parameters and the results also indicate that the percentage of dpep porphyrins decreases through migration

field evaluation of some sand transport models fluorescent tracer procedures originally developed for research on fluvial sediment movement were used to monitor the movement of three commercially purchased sands in a natural dune environment results were compared with estimates of transport rates from three theoretical models estimates from models by bagnold 1941 and hsu 1971 were larger by as much as one order of magnitude than the rates observed in the tracer study the model of a a kadib 1965 provided closer correspondence to observed transport rates for medium sand mean diam 0 653 mm but underestimated rates for coarse sand mean diam 0 992 mm

air flow over foredunes and implications for sand transport more than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed wind flow over the foredunes is studied by means of the relative wind speed the ratio between wind speed at a certain location and the reference wind speed at the same height relative wind speeds appear to be independent of general wind speed but dependent on wind direction for perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness accelerations dominate over decelerations on the seaward slope the pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes but the magnitudes differ an increase in foredune height from 6 to 10m leads to an increase in speed up near the top of the seaward slope from 110 to 150 per cent during onshore wind but further increase of foredune height from 10 to 23 m appears to have little effect due to increased roughness and deflection of flow topography also influences the direction of the flow between beach and top the flow deflects in the direction of the normal during onshore winds during offshore winds the flow is deflected to the parallel near the dunefoot deflection is always in the direction of the parallel and increases with steeper topography the maximum deflection near the dunefoot was 90 over a 23 m high dune observed during offshore winds patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations owing to speed up on the seaward front of the foredune sand transport capacity of the wind increases which results in erosion if vegetation is absent during strong onshore wind sand is lifted near the dunefoot and moves over the foredune in suspension during weaker winds vertical wind velocities do not exceed fall velocities of the sand grains and most of the sand is deposited near the dunefoot

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

rates of aeolian transport on a beach in a temperate humid climate short term field measurements of aeolian transport using a saltiphone indicate that actual rates of transport deviate considerably from the potential rates predicted by transport equations when examined in detail however potential rates are approached during special conditions mostly when the wind blows offshore parallel or slightly oblique to the beach and relative humidity is below 85 also the potential rates of transport may be approached when wind speeds considerably exceed threshold speed even during showers the main cause of the large deviation of actual from potential rates is in the absence of transport during very wet conditions prolonged rainfall regardless of wind speed and the variation of threshold velocity with time the threshold velocity increases during wet conditions with onshore winds or because of the presence of algae therefore potential transport is defined as the transport optimum to predict the actual rates of transport accurately insight into the variation of the threshold velocity is essential aeolian transport of sand seems to be related to moderate events and not to extreme events conforming to the principle of magnitude and frequency

the morphology and evolution of coronae on venus coronae on venus are large circular to ovoidal surface features that have distinctive tectonic volcanic and topographic expressions they range in diameter from less than 200 km to at least 1000 km new data from the magellan spacecraft have shown coronae to be among the dominant tectonic forms on the planet and have revealed their morphology in unprecedented detail typical coronae are dominated by concentric tectonic features and have a raised rim a central region higher than the surounding plains but in many instances lower than the rim and commonly a peripheral depression or moat some coronae also show significant amounts of radial tectonic structure and in most cases this predates the concentric features in addition there are other features on venus recognized for the first time in magellan data that consist of domical rises with intense radial tectonic patterns and little or no concentric structure all of these features commonly are associated with moderate to large quantities of volcanism in fact some radially fractured domes have undergone so much volcanism that volcanic construction appears to have played a significant role in establishing their topography we explore a model of corona formation that links these forms into a genetic sequence the model begins with the ascent of a mantle diapir upward mantle flow driven by its ascent forces the lithosphere above the diapir upward producing a gentle dome with a radiating pattern of extensional fractures as the diapir impinges on the underside of the lithosphere it flattens and spreads transforming the uplift to a more flat topped shape in this flattened near surface configuration the diapir can cool rapidly with the resultant loss of buoyancy the raised plateau can relax to form a central sag a raised rim and a depressed moat concentric tectonic features develop primarily during the latter stages of corona formation and hence are best preserved on mature coronae volcanism takes place during all phases of the uplift and may diminish as the relaxation occurs our analyses to date suggest that this scenario is broadly consistent with many of the coronae on venus however there is enormous diversity in corona morphology and features are present that require substantial deviations from this simple model in particular some circular depressions appear corona like in synthetic aperature radar images but may in fact be large calderas some of the variations observed in corona morphology may ultimately be interpretable in terms of variations in the behavior of individual diapirs and in the local properties of the venusian lithosphere

the influence of rainfall on transport of beach sand by wind this paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments although sediment transport by splash is of secondary importance on coastal dunes splash saltation processes can move sediments in conditions where no motion is predicted by aeolian processes the effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler in general an increase of particle movement by wind at the sensor heights was observed during rainfall rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface the influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles

modelling aeolian sand transport using a dynamic mass balancing approach abstract knowledge of the changing rate of sediment flux in space and time is essential for quantifying surface erosion and deposition in desert landscapes whilst many aeolian studies have relied on time averaged parameters such as wind velocity u and wind shear velocity u to determine sediment flux there is increasing field evidence that high frequency turbulence is an important driving force behind the entrainment and transport of sand at this scale of analysis inertia in the saltation system causes changes in sediment transport to lag behind de accelerations in flow however saltation inertia has yet to be incorporated into a functional sand transport model that can be used for predictive purposes in this study we present a new transport model that dynamically balances the sand mass being transported in the wind flow the dynamic mass balance dmb model we present accounts for high frequency variations in the horizontal u component of wind flow as saltation is most strongly associated with the positive u component of the wind the performance of the dmb model is tested by fitting it to two field derived namibia s skeleton coast datasets of wind velocity and sediment transport i a 10 min 10 hz measurement resolution dataset ii a 2 h 1 hz measurement resolution dataset the dmb model is shown to outperform two existing models that rely on time averaged wind velocity data e g radok 1977 dong et al 2003 when predicting sand transport over the two experiments for all measurement averaging intervals presented in this study 10 hz 10 min the dmb model predicted total saltation count to within at least 0 48 whereas the radok and dong models over or underestimated total count by up to 5 50 and 20 53 respectively the dmb model also produced more realistic less peaky time series of sand flux than the other two models and a more accurate distribution of sand flux data the best predictions of total sand transport are achieved using our dmb model at a temporal resolution of 4 s in cases where the temporal scale of investigation is relatively short on the order of minutes and at a resolution of 1 min for longer wind and transport datasets on the order of hours the proposed new sand transport model could prove to be significant for integrating turbulence scale transport processes into longer term macro scale landscape modelling of drylands

geophysical models for the formation and evolution of coronae on venus coronae are large circular features on venus characterized by an annulus of concentric tectonic features interior fracturing volcanism and generally upraised topography they are suggested to form over sites of mantle upwelling and modified by subsequent gravitational relaxation we examine this proposition using two geophysical models to determine whether and under what conditions these mechanisms can produce the topography and tectonics exhibited by coronae in the magellan altimetry data and radar images our results show that mantle diapirism can produce the domical topography of novae which may be coronae in the earliest stage of formation the model stresses induced at the surface by a mantle diapir imply the formation of radially oriented extensional fracturing as observed in novae the dimensions of novae indicate that the diapirs responsible for them are smaller than about 100 km in radius and that the elastic lithosphere is less than 32 km thick diapirs that have reached the top of the mantle are expected to spread and flatten producing plateaulike rather than domical topography we model a flattened diapir at the top of the mantle and show that it will result in plateaulike uplift the volume of the flattened model diapir is similar to that of the spherical diapirs derived for novae we model gravitational relaxation of isostatically uncompensated plateaus and show that they relax to the topographic forms associated with coronae and that the model stresses are consistent with the development of the annulus of tectonic features around coronae

effect of source width and tidal elevation changes on aeolian transport on an estuarine beach data from a moderate energy meso tidal beach on the east side of delaware bay new jersey usa revealed the significance of both beach width as a source for aeolian transport and the effect of tidal rise on source width wind speeds averaged over 17 1 min recorded 6 m above the crest of a 0 5 m high dune ranged from 11 6 to 12 7 m s 1 during the experiment the highest observed rate of transport on the beach was 0 0085 kg m 1 s 1 monitored at rising low tide when the average wind speed was 11 6 m s 1 across 0 35 mm diameter surface sediments the wind direction was oblique to the shoreline creating a source width of 34 m the reduction in the width of the beach as a source for aeolian transport during rising tide was approximately arithmetic whereas the reduction in volume of sediment trapped was exponential aeolian transport effectively ceased when source width was less than 8 m wind conditions moisture content of the surface sediments and presence of binding salts did not appear to vary dramatically and no coarse grained lag deposit formed on the surface of the beach the decrease in rate of sediment trapped through time in the tidal cycle is attributed to differences in source width sediment deposited in the litter behind the active beach by strong winds during the rising tide was eroded during the high water period by the high waves and storm surge generated by these winds and net losses of sediment were observed despite initial aeolian accretion

on the efficiency of vertical array aeolian field traps the efficiency of three vertical array field traps for measuring the distribution of aeolian mass transport with height was compared with measurements with an isokinetic trap the vertical traps seem to work adequately efficiency 80 at heights greater than 15 mm above the bed closer to the bed however the open array trap catches about 70 the two continuous arrays only about 50 because most of the transport takes place close to the surface the overall efficiency of the field traps ranges from 50 to 70 based on these wind tunnel tests we have developed a low single compartment wedge shaped trap its shape in combination with flow straighteners at the entrance minimizes stagnation effects so that the efficiency is 80 our data indicate that with the wedge trap used in combination with the vertical array aberdeen trap we can sample mass transport in the field during periods with unidirectional winds with an overall efficiency of the order of 80

recalibrating aeolian sand transport models a quality controlled data set comprising measurements of aeolian sand transport rates obtained at three disparate field sites is used to evaluate six commonly employed transport rate models those of bagnold kawamura zingg owen hsu and lettau and lettau and to recalibrate the empirical constants in those models shear velocity estimates were obtained using the von karman constant and an apparent von karman parameter models were recalibrated using non linear regression and non linear regression with least squares lines forced through axes origins recalibration using the apparent von karman parameter and forced regression reduced the empirical constants for all models the disparity between the predictions from the different models is reduced from about an order of magnitude to about a quarter of an order of magnitude the recalibrated lettau and lettau model provided the greatest statistical agreement between observed and predicted transport rates with a coefficient of determination of 0 77 evaluation of the results suggests that our estimations of threshold shear velocity may be too slow causing errors in predicted transport rates copyright 2012 john wiley sons ltd

venus tectonics initial analysis from magellan radar imaging and altimetry data from the magellan mission have revealed a diversity of deformational features at a variety of spatial scales on the venus surface the plains record a superposition of different episodes of deformation and volcanism strain is both areally distributed and concentrated into zones of extension and shortening the common coherence of strain patterns over hundreds of kilometers implies that many features in the plains reflect a crustal response to mantle dynamic processes ridge belts and mountain belts represent successive degrees of lithospheric shortening and crustal thickening the mountain belts also show widespread evidence for extension and collapse both during and following crustal compression venus displays two geometrical patterns of concentrated lithospheric extension quasi circular coronae and broad rises with linear rift zones both are sites of significant volcanism no long large offset strike slip faults have been observed although limited local horizontal shear is accommodated across many zones of crustal shortening in general tectonic features on venus are unlike those in earth s oceanic regions in that strain typically is distributed across broad zones that are one to a few hundred kilometers wide and separated by stronger and less deformed blocks hundreds of kilometers in width as in actively deforming continental regions on earth

a field experiment on the role of small scale wind gustiness in aeolian sand transport estimates of aeolian sand transport generally use an average wind speed to assess the wind energy to determine if variation in small scale wind gustiness on the order of several seconds duration has a significant effect on sand movement detailed field measurements were made of wind speed and transport rate average wind speed and several gust parameters were derived from the wind data the results indicate that small scale gust information does not improve prediction of transport rates

effects of biodegradation upon porphyrin biomarkers in upper mississippian tar sands and related oils southern oklahoma abstract organic molecules present in oils which show a structural relationship to their biological precursors are referred to as biomarkers these compounds are becoming widely used in oil exploration for making oil oil oil source rock correlations and undertaking maturation and migration studies in basin analysis treibs first discovered the presence of porphyrins in oils shales and coals over 50 years ago porphyrins are predominantly derived from chlorophyll precursors present in plants and bacteria studies of changes in porphyrin distributions with increasing maturation due to the effects of increased time of burial and temperature have been performed however little is known as to how their distributions change with migration biodegradation or water washing of oils in the present study 16 tar sand samples were extracted from drill core at depths ranging from 16 to 256 ft obtained from a tar sand quarry in the ardmore basin carter county oklahoma surrounding oil samples and possible source rocks have also been analyzed to determine the source of the oil in the tar sands the effects of biodegradation on the porphyrin distributions can be discerned from the effects of migration and maturation by comparing other biomarker distributions within the sands related oils and suspected source rocks more biodegradation of the tar sand samples can be observed within the alkane and other biomarker distributions the relative effects of biodegradation on biomarkers such as alkanes steranes and terpanes have been well documented by using this information it is possible to determine the extent of biodegradation or water washing necessary to alter the porphyrin distributions less

mobility of a remobilised parabolic dune in kennemerland the netherlands abstract a parabolic dune in the netherlands was remobilised in december 1998 by removing vegetation and soil the main aim of the experiment was ecological to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes if processes can be reactivated at coarse scale periodic rejuvenation of the landscape over the long term is possible without the need for managers to interfere further the experiment provides the opportunity to address another important question can large parabolic dunes in the netherlands be mobile in the present climate mobility of the dune is investigated by means of erosion pins aerial photography and measurement of cross sections activity indices are derived from erosion pin recordings and correlated to weather conditions from 1999 to 2001 displacement of the dune ranged from 0 to 12 m in east northeasterly direction activity of the dune is related to wind conditions but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods periods with extreme wind speeds resulted in much less geomorphic change than expected

venus volcanism initial analysis from magellan data magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of venus high resolution imaging data reveal evidence for intrusion dike formation and cryptodomes and extrusion a wide range of lava flows also observed are thousands of small shield volcanoes larger edifices up to several hundred kilometers in diameter massive outpourings of lavas and local pyroclastic deposits although most features are consistent with basaltic compositions a number of large pancake like domes are morphologically similar to rhyolite dacite domes on earth flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas perhaps komatiites may be present volcanism is evident in various tectonic settings coronae linear extensional and compressional zones mountain belts upland rises highland plateaus and tesserae volcanic resurfacing rates appear to be low less than 2 km 3 yr but the significance of dike formation and intrusions and the mode of crustal formation and loss remain to be established