latitude dependent nature and physical characteristics of transverse aeolian ridges on mars 1 narrow angle images from the mars orbiter camera moc have revealed the common occurrence of small scale 100 m wavelength bright transverse aeolian ridges tars on the surface of mars moc images were used to assess the broad distribution of tars from 90 n to 90 s between 180 e and 240 e to investigate their relationship to latitude elevation thermal inertia geologic units local slopes and surface roughness out of 5112 examined images from the primary mission 520 10 contain evidence of tars 92 of the images with tars are located between 50 latitude and very few occur in the middle to upper latitudes or polar regions of either hemisphere tars are observed at elevations from 5 km to 3 km with the highest frequency 26 between 1 and 0 km there is no systematic relationship between the distribution of tars and global thermal inertia measurements most tars occur in geologic units associated with the channel system materials 39 and the olympus mons aureole 33 at a length scale of 1 85 km pixel the average local slopes for images with and without tars are 1 92 and 1 36 respectively of the parameters investigated the latitudinal trend of tars in both hemispheres appears to be predominantly related to surface roughness with a positive linear correlation between the surface roughness of geologic units and frequency of tars r2 0 87 factors affecting the semiglobal distribution of tars are likely related to the climate and wind regimes in which they formed but do not provide definitive evidence for either saltation or reptation formation mechanisms

wind regime sediment transport and landscape dynamics at a mars analogue site in the andes mountains of northwestern argentina abstract the puna plateau of northwestern argentina is a promising region for analogue investigations of martian aeolian processes owing to its high altitude low atmospheric pressure aridity geology and widespread granular and bedrock aeolian landforms despite a growing body of research about the region s enigmatic aeolian landforms little is known about the contemporary aeolian environment processes and landscape dynamics to address this gap we used a combination of modelled weather data satellite imagery and field measurements to characterize the wind regime aeolian sediment transport and allied surface changes the study focused on the campo de piedra pomez cpp a volcanic landscape with a variety of mars analogue landforms gravel mantled megaripples yardangs ventifacts periodic bedrock ridges and aeolian rat tails modelled weather data from the european center for medium range forecasting s era interim reanalysis dataset confirm the contemporary dominance of northwesterly winds in this region consistent with the primary orientation of yardangs these data also indicate the presence of less frequent southeasterly winds which may explain why re entrant profiles are observed on the southeast flanks of a small portion of the yardang population and why some aeolian rat tails point to the northwest observations from multi temporal satellite imagery indicate that deposition and displacement of small sediment patches overlying ignimbrite bedrock is relatively common across the region samples retrieved from sediment traps deployed over one year in the region suggest a broad range of particle densities are mobilized by wind which implies a wide range of wind speed for fluid entrainment conventional aeolian transport models do not consider the effects of particle density variations on transport processes however in areas with multiple density sediment present our results point towards a need for aeolian models to consider density when quantifying and qualifying sediment transport

rheology and rupture of homogeneous silicate liquids at magmatic temperatures homogeneous silicate liquids have a newtonian rheology under conditions of modest stress but under relatively high stress or otherwise imposed high rates of deformation their viscosity may become non newtonian before the onset of rupture this behavior has been discussed semi empirically as well as in terms of the maxwell model liquid here it is shown that the configurational entropy theory for the occurrence of the glass transition can also explain this non newtonian rheology of silicate liquids ranging in composition from silica rich to silica poor the pressure and temperature dependence of the transition from newtonian to non newtonian flow is discussed qualitatively geological applications are indicated fragmentation of silicate liquids takes place when the glass transition is crossed and the liquid has become solid like experimental evidence indicates that the rupture strength is only slightly larger than the stress needed to cause the onset of non newtonian rheology

transverse aeolian ridges tars on mars aeolian processes are probably the dominant ongoing surface modification process on mars as demonstrated by observations of dunes ripples yardangs ventifacts wind streaks dust devils and dust storms large dark dunes ldds are particularly common and were first recognized in the 1960 s from mariner data however another population of smaller often brighter ripple like aeolian bed forms that are morphologically distinct from ldds has been observed in recent higher resolution images calculations of saltation path length under martian conditions suggest these small bed forms could have formed as small barchanoid dunes or as mega ripples also known as granule ripples these features have therefore been called transverse aeolian ridges tars as this label has no genetic inference we have begun a study of tars that examines all high resolution mars orbiter camera data 1 5 to 8 m pixel resolution in a 45o longitude wide pole to pole swath we aim to determine the geographic distribution of tars assess whether they are active and to identify possible sediment sources we have already made some key observations first we present a new classification of tar deposits based on crest ridge morphology of individual forms and the size and degree of topographic control of the entire sediment mass second we present associations of tars with ldds slope streaks dust devils tracks and small impact craters that provide clues as to whether tars are currently active finally we present preliminary pole to pole survey results for the northern hemisphere that show clusters of tar deposits in the low latitudes suggesting possible unique sediment sources in these regions

megaripple flattening due to strong winds abstract megaripples in nahal kasuy in the southern negev desert of israel are characterized by a mean wavelength of about 70 cm and by a bimodal distribution of coarse and fine particle sizes the latter property being a pre requisite for their formation in our three year project megaripple development was monitored using a digital elevation model dem constructed from above ground stereo digital photographs temporal dynamics of wind power drift potential dp were measured and grain size analyses were performed on samples taken from different parts of the megaripple the coarse grains that protect the crest enable the ripple to grow but when ripple height becomes too high the bed shear stress increases thus allowing the wind to move the armoring layer when this happens during strong wind storms the megaripple will flatten and even disappear as was observed in our field study we present measurements that for the first time directly show the megaripple to normal ripple transition and we suggest two possible physical processes as potential causes of this phenomenon megaripple flattening can occur either when the wind exceeds the fluid threshold for a sufficient length of time or after a sequence of storms with winds blowing from the same direction

geochronology and stratigraphy of the ignimbrites from the 21 30 s to 23 30 s portion of the central andes of northern chile the central volcanic zone cvz of the andes which extends from 14 to 28 s is one of the largest provinces of late tertiary to recent ignimbrite volcanism in the world in the 21 30 s to 23 30 s portion of the cvz in northern chile ignimbrite volcanism was initiated at the beginning of the late miocene 10 4 ma ago and continued until the recent the stratigraphy is dominated by the products of five major dacitic ignimbrite eruptions 100 km3 the artola ignimbrite member 9 4 ma the sifon ignimbrite member 8 3 ma the pelon ignimbrite member 5 5 ma the puripicar ignimbrite member 4 2 ma and the atana ignimbrite member 4 1 ma at least three of these represent only portions of larger ignimbrite sheets erupted from centres of sw bolivia two of the ignimbrites the sifon and atana ignimbrites must represent erupted volumes in excess of 1000 km3 each the major units which represent 90 of the total volume of ignimbrite in this area are intercalated with smaller 50 km3 less extensive volcanic units some of which were erupted from source structures within the study area the upper tertiary to recent volcanic stratigraphy has been revised using the large ignimbrites as the major stratigraphic horizons the ignimbrite formations can be divided into two groups on a geographic basis those in the northern and central portions of the study area are known as the san bartolo group while those in the southern portion belong to the silapeti group these two groups appear to be contemporaneous although the silapeti group may represent a period of ignimbrite volcanism which was initiated later about 6 ma ago the ignimbrite formation of sw bolivia and the punense arancaniano formation of nw argentina are equivalent to the san bartolo and silapeti groups based on correlation of the stratigraphy into adjacent areas in sw bolivia and nw argentina the beginning of the late miocene 10 4 ma marks the onset of the most intense phase ignimbrite volcanism in the cvz this phase of volcanism is suggested to be the result of crustal melting in response to crustal thickening during the quechua phase of deformation and subduction approximately 10 000 km3 of ignimbrite erupted over a period of 9 ma in the 21 30 23 30 s portion and led to the development of a major ignimbrite province

distinct erosional progressions in the medusae fossae formation mars indicate contrasting environmental conditions abstract the form of erosional remnants of the medusae fossae formation mff on mars provide evidence of their development progression and implicate two spatially distinct environments in the equatorial regions of mars ubiquitous yardangs are clearly the product of strong unidirectional winds acting over time on variably indurated deposits yardang orientation is used as a proxy to map regional and local wind direction at meso scale resolution in other more limited areas not subjected to strong unidirectional winds randomly oriented kilometer scale mesas and buttes are found to be remnants of progressive cliff recession through mass wasting as support is lost from within the mff lithology at its margins the differing processes that dominate the formation of the distinctive landforms have implications for meso scale variations in climate that remain unresolved by current modeling efforts additionally the variability of erosional forms within the deposit emphasizes the overall complexity of this extensive formation

wind formed gravel bed forms wright valley antarctica 1 bed forms composed of gravel size particles 50 of particles 4 mm are observed in the wright valley of the mcmurdo dry valley system in antarctica these bed forms are characterized by a very asymmetrical shape with a mean aspect ratio of 0 025 standard deviation 0 005 mean wavelength of 2 7 m 0 49 m and a mean height of 0 06 m 0 01 m particle size analysis of the bed form sediments shows bimodality with a peak near 9 mm and another between 0 5 mm and 0 25 mm time integrated sediment trap samples of horizontal saltation and creep flux indicate the flux of particles 4 mm during the two year monitoring period was extremely low measurements of the horizontal displacement of tracer particles 14 mm 12 mm 10 mm 8 mm and 6 mm diameter placed onto the bed forms corroborate the low particle flux measurements and limited movement of particles the bed forms share form and grain size characteristics with both ripples and mega ripples showing poor sorting of particles across a single wavelength except for a slight coarsening at the crest similar to ripples but their sinuosity suggest that transverse instabilities affect their formation similar to mega ripples based on the data for the prevailing environmental conditions it can be argued that the wright valley form is an expression of gravel particles moved solely by highly intermittent creep processes this also argues for the need for a very long period of time for their evolution on the order of centuries

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

transverse aeolian ridges tars on mars ii distributions orientations and ages transverse aeolian ridges tars 10 m scale ripple like aeolian bedforms with simple morphology are widespread on mars but it is unknown what role they play in mars wider sediment cycle we present the results of a survey of all mars global surveyor narrow angle images in a pole to pole study area 45 longitude wide following on from the classification scheme and preliminary surveys of balme et al balme m r berman d c bourke m c zimbelman j r 2008a geomorphology 101 703 720 and wilson and zimbelman wilson s a zimbelman j r 2004 j geophys res 109 e10 doi 10 1029 2004je002247 we searched more than 10 000 images and found that over 2000 reveal at least 5 areal cover by tars the mean tar areal cover in the study area is about 7 3 in the northern hemisphere and 11 in the southern hemisphere but tars are not homogenously distributed they are concentrated in the mid low latitudes and almost absent poleward of 35 n and 55 s we found no clear correlation between tar distribution and any of thermal inertia kilometer scale roughness or elevation we did find that tars are less common at extremes of elevation we found that tars are most common near the equator especially in the vicinity of meridiani planum in which area they have a distinctive barchan like morphology and in large southern hemisphere impact craters tars in the equatorial band are usually associated with outcrops of layered terrain or steep slopes hence their relative absence in the northern hemisphere tars in the southern hemisphere are most commonly associated with low albedo intercrater dune fields we speculate that the mid latitude mantling terrain e g mustard j f cooper c d rifkin m k 2001 nature 412 411 414 kreslavsky m a head j w 2002 j geophys res 29 15 doi 10 1029 2002gl015392 could also play a role in covering tars or inhibiting saltation we compared tar distribution with general circulation model gcm climate data for both surface wind shear stress and wind direction we performed gcm runs at various obliquity values to simulate the effects of changing obliquity on recent mars climate we found good general agreement between tar orientation and gcm wind directions from present day obliquity conditions in many cases but found no good correlation between wind shear stress and tar distribution we performed preliminary high resolution crater count studies of tars in both equatorial and southern intracrater dunefield settings and compared these to superposition relationships between tars and large dark dunes our results show that tars near dunefield appear to be younger than tars in the equatorial regions we infer that active saltation from the large dunes keeps tars active but that tars are not active under present day condition when distal to large dunes perhaps supporting the interpretation that tars are granule ripples we conclude that local geology rather than wind strength controls tar distribution but that their orientation matches present day regional wind patterns in most cases we suggest that tars are likely most perhaps only active today when they are proximal to large dark dune fields

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

ignimbrites of amazonis planitia region of mars a series of postulated ignimbrite units is mapped in the amazonis memnonia and aeolis quadrangles of mars the units cover about 2 2 106 km2 within a broad but discontinuous and irregular belt trending east west along the highland lowland boundary the ignimbrites overlie parts of the western and southern aureole materials of olympus mons but are embayed in places by the lava plains of the lowlands stratigraphic relations between the basalt flows from the tharsis montes region and the ignimbrites are not clearly defined crater counts suggest that the younger ignimbrites postdate the lava flows crater counts per square kilometer for the ignimbrites range from 7 29 1 95 10 4 to 6 36 2 01 10 5 for craters larger than 1 km in diameter the ignimbrite materials form thick 100 m extensive relatively flat sheets that are smooth to grooved or gently undulating grooved surfaces appear to be yardangs and in most places are not alined with prevailing wind directions the seven mapped ignimbrite units are characterized by morphologic expression stratigraphic position and crater counts similarities to ignimbrites in the pancake range of central nevada include 1 rounded patches of smooth high albedo nonwelded material superposed on jointed low albedo welded material 2 local complementary joint sets in welded materials and 3 thick flow sheets of great areal extent that follow but subdue underlying topography four major eruptive centers occur in areas where units are thickest and where a dominant nnw sse structural trend is expressed locally by unit margins elongate collapse features and normal faulting a minimum volume of 3 85 106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations

the largest wind ripples on earth reply we thank de silva 2010 1 for the opportunity to discuss the origin of the unique megaripples mr found on the puna plateau forman and krohling were invited as co authors of this reply because we produced new data supplied here de silva suggests that the genetic relationship inferred by

clay mineralogy cation exchange capacity and specific surface area of loess soils with different volcanic ash contents the loessical soils of the semiarid argentinean pampas sap contain variable amounts of volcanic ashes their influence on the mineral composition and some physicochemical properties of soils like soil specific surface area ssa and cation exchange capacity cec have been still not elucidated because of that we analyzed 24 topsoil samples 0 to 20 cm of soils with high and low volcanic ashes contents for clay mineralogy and its influence on soil chemical and physical properties and cec and ssa results showed that ash enriched soils were placed to the south and ash free soils to the north east of the sap in agreement with the volcanic ash deposition pattern of 1932 quizapu vocano eruption mineralogy of the clay fraction was dominated by amorphous minerals and less crystallized and expansible smectites in ash enriched soils and by illites in ash free soils no differences in crystallinity or expansibility were found between montmorillonites of ash free and ash enriched soils fine sized clays 0 2 m were dominated by illites and illite montmorillonite intergrades in ash free soils and by amorphous materials in ash enriched soils such results indicated that montmorillonites tend to form more when volcanic ashes are present but their crystallinity and expansibility do not change with ashes content ssa was positively related with silt contents in both ash free and ash enriched soils r2 0 70 p 0 05 the clay fraction 2 m explained only 9 of ssa variability and the fine clay fraction 0 2 um did not affect ssa the influence of silt on ssa was attributed to the existence of 2 1 minerals in the silt fraction these results also indicated that ash contents did not influence ssa cec correlated positively with clay r2 0 67 p 0 001 in ash enriched soils and with organic matter in ash free soils r2 0 837 p 0 001 but it did not correlate with fine clay contents in any of both soil types these trends were explained on the basis of the higher cec conferred by smectites in ash enriched soils and by om in ash free soils it can be deduced that soil degradation processes producing losses of fine sized particles like wind or water erosion will decrease ssa in both the ash enriched and the ash free soils but only cec in ash enriched soils organic matter losses due to excessive cultivation will decrease cec in ash free soils

high resolution investigations of transverse aeolian ridges on mars abstract transverse aeolian ridges tars are the most pervasive aeolian feature on mars their small size requires high resolution data for thorough analyses we have utilized mars reconnaissance orbiter mro context camera ctx and high resolution image stereo experiment hirise images along with mro compact reconnaissance imaging spectrometer for mars crism spectroscopic data to study tars in detail tar deposits along with related dark dune material and layered terrains have been mapped in six study areas in order to identify sediment pathways and determine whether tars are sourced locally or from global wind borne materials tar morphology and orientation were mapped in grids within each study area the results show that tars are probably locally sourced we constructed four hirise digital terrain models dtms to measure tar heights widths spacing areas symmetry and to calculate sediment volumes results show that tars have average heights of 1 5 m are very symmetrical and are similar in form to terrestrial megaripples orthorectified hirise images taken 3 years apart were analyzed for tar movement and none was found superposed craters on equatorial tars give ages of 2 ma suggesting that these are relatively ancient and generally inactive aeolian deposits crism data were analyzed over tar deposits dark dune material and light toned terrains although the surfaces were somewhat obscured by dust cover the results did not show any remarkable difference between tars and other deposits we conclude that tars may be sourced from local materials and form in a similar way to terrestrial megaripples

paleo eolian dynamics in the andean plateau inferences from sedimentology of fossil and modern dunes fil lopez steinmetz romina lucrecia universidad nacional de jujuy instituto de ecorregiones andinas consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet salta instituto de ecorregiones andinas argentina universidad nacional de jujuy argentina consejo nacional de investigaciones cientificas y tecnicas argentina

the albano maar lake colli albani volcano italy recent volcanic activity and evidence of pre roman age catastrophic lahar events abstract the evaluation of volcanic hazard in the roman hinterland related to the quiescent colli albani volcano has recently been the subject of renewed attention and several interpretations by many authors however very little was known of the recent history of the volcano making such interpretations rather speculative the most recent activity of colli albani volcano originated from the albano polygenetic maar lake which erupted several phreatomagmatic units the most recent of which the peperino albano ignimbrite has been dated at around 25 ka an area of several square kilometers centered around albano lake is presently the site of shallow and frequent seismic activity and gaseous emission as well as hydrothermal activity and is therefore considered the most prone to geologic hazards this paper presents new stratigraphic and geomorphologic data as well as age determinations that allow rejuvenation of the most recent activity of the colli albani volcano and particularly the albano maar lake to the holocene this study allows for the first time to identify a potential hazard related to the albano maar lake withdrawal interpreted to be related to endogenous causes namely co 2 emission the main results of the study are 1 the peperino albano is not as is generally believed the last phreatomagmatic eruption from the colli albani volcano a previously unrecognized phreatomagmatic surge deposit has been identified overlying the paleosol at the top of the peperino albano and related lahar deposits 2 two lahar deposits separated by paleosols top the stratigraphic succession and are dispersed only to the nw corresponding to the lowest point of the maar rim indicating that catastrophic hydrologic events occurred at the albano lake in recent times rapid and substantial lake level variations and lake withdrawal are reported by roman historians and recorded by the stratigraphy of the albano lake lacustrine sediments 3 microfracturing related to seismic energy release is linked to sudden variation of co 2 flow and upwelling of hydrothermal fluids these occurrences across the lake are the likely causes that triggered during holocene several episodes of lake withdrawal rising the water table and probably triggering convective rollover of the lake water

cross sectional profiles of sand ripples megaripples and dunes a method for discriminating between formational mechanisms cross sectional profiles of sand ripples megaripples and sand dunes provide a useful tool for discriminating between formation by ripple and dune processes feature width defined as the basal break in slope along the profile to either side of the crest represents a good standard for comparison of profile attributes across more than three orders of magnitude aspect ratio height width as a function of log width separates measurements into clusters representing differing mechanisms of formation scaling both height and distance for individual profiles by feature width facilitates comparison of profile shapes across three orders of magnitude in width the data presented here should prove useful for evaluating possible mechanisms of origin for aeolian features observed remotely including on planetary bodies copyright 2012 john wiley sons ltd

analysis of transverse aeolian ridge profiles derived from hirise images of mars photoclinometry was used to analyze selected high resolution imaging science experiment hirise images of transverse aeolian ridges tars on mars sixty mars profiles have been assessed and a summary of their morphologic characteristics compiled measurements collected quantified the symmetry of the feature the curvature of the crest flank slopes width height and several comparative ratios results show that small tars have physical characteristics generally similar to measurements obtained from lower resolution images of mars the hirise image data allow for much improved sampling along each feature the improved resolution reveals relatively few features not seen in earlier studies but is well suited for topographic sampling measured tar profiles when scaled by the width of the feature can be compared to similarly scaled profiles for terrestrial dunes and megaripples published 2012 this article is a u s government work and is in the public domain in the usa

soils of eagle crater and meridiani planum at the opportunity rover landing site the soils at the opportunity site are fine grained basaltic sands mixed with dust and sulfate rich outcrop debris hematite is concentrated in spherules eroded from the strata ongoing saltation exhumes the spherules and their fragments concentrating them at the surface spherules emerge from soils coated perhaps from subsurface cementation by salts two types of vesicular clasts may represent basaltic sand sources eolian ripples armored by well sorted hematite rich grains pervade meridiani planum the thickness of the soil on the plain is estimated to be about a meter the flatness and thin cover suggest that the plain may represent the original sedimentary surface

investigation of three dimensional wind flow behaviour over coastal dune morphology under offshore winds using computational fluid dynamics cfd and ultrasonic anemometry the behaviour of offshore directed winds over coastal dune and beach morphology was examined using a combination of modelling 3 d computational fluid dynamics cfd and field measurement both model simulations and field measurements showed reversal of offshore flows at the back beach and creation of an onshore sediment transport potential the influence of flow reversals on the beach dune transport system and foredune growth patterns has previously received little attention detailed wind flow measurements were made using an extensive array of mast mounted 3 d ultrasonic anemometers 50 hz arranged parallel to the dominant incident wind direction large eddy simulation les of the offshore wind flow over the dune was conducted using the open source cfd tool openfoam the computational domain included a terrain model obtained by airborne lidar and detailed ground dgps measurements the computational grid 22 million cells included localized mesh refinement near the complex foredune terrain to capture finer details of the dune morphology that might affect wind flows on the adjacent beach measured and simulated wind flow are presented and discussed the cfd simulations offer new insights into the flow mechanics associated with offshore winds and how the terrain steering of wind flow impacts on the geomorphological behaviour of the dune system simulation of 3 d wind flows over complex terrain such as dune systems presents a valuable new tool for geomorphological research as it enables new insights into the relationship between the wind field and the underlying topography the results show that offshore and obliquely offshore winds result in flow reversal and onshore directed winds at distances of up to 20m from the embryo dune toe the potential geomorphological significance of the findings are discussed and simple calculations show that incoming offshore and obliquely offshore winds with mean velocities over 13m s 1 and 7m s 1 respectively have the potential to create onshore directed winds at the back beach with mean velocities above 3 3m s 1 these are above the threshold of movement for dry sand and support previous conclusions about the significance of offshore winds in dune and beach budget calculations

origin of the medusae fossae formation mars insights from a synoptic approach 1 the geologic origin of the medusae fossae formation mff has remained a mystery despite three decades of research to better constrain its formation an in depth analysis of observations made in the literature was combined with a new survey of over 700 mars orbiter camera narrow angle images of the mff to identify morphologic characteristics and material properties that define this formation as a whole while previous work has identified clear agreement on some characteristics our analysis identifies yardangs collapse features and layering as pervasive features of the mff whereas collapse features and layering may implicate several different physical and chemical processes yardangs provide vital information on material properties that inform about mechanical properties of the mff lithology aspect ratios of megayardangs range from 3 1 to 50 1 and slope analyses reveal heights of up to 200 m with cliffs that are almost vertical other yardangs show lower aspect ratios and topographic profiles these characteristics coupled to the presence of serrated margins suggest that mff lithology must be of weakly to heavily indurated material that lends itself to jointing the characteristics and properties of the mff are inconsistent with those of terrestrial pyroclastic fall deposits or loess but are in common with large terrestrial ignimbrites a hypothesis that explains all key observations with a single mechanism yardang fields developed in regionally extensive ignimbrite sheets in the central andes display morphologic characteristics that correlate with degree of induration of the host lithology and suggest an origin by pyroclastic flow for the mff

planet wide sand motion on mars prior to mars reconnaissance orbiter data images of mars showed no direct evidence for dune and ripple motion this was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low density atmosphere we show that many sand ripples and dunes across mars exhibit movement of as much as a few meters per year demonstrating that martian sand migrates under current conditions in diverse areas of the planet most motion is probably driven by wind gusts that are not resolved in global circulation models a past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains

gravel mantled megaripples of the argentinean puna a model for their origin and growth with implications for mars gravel megaripples in the puna of argentina are the most extreme aeolian megaripples on earth and are useful analogs for aeolian processes on mars field observations supplemented by experimental and numerical constraints on wind characteristics and aeolian transport reveal their conditions of formation and growth to be an aeolian geomorphology perfect storm the bedforms are formed on a substrate of weakly indurated ignimbrite aeolian deflation of which yields a bimodal lag of lithics and pumice clasts onto an undulating surface under normal wind conditions in this region the lithics are organized into bedforms on local upslopes and highs through creep induced by the impact of saltating sand and pumice the gravel bedforms grow through shadowing and trap sand and silt that is gradually kinetically sieved down to lift the gravel mantle upwards to form the megaripples these observations connote that the largest features are not ripples in the sense of migrating bedforms but rather nucleation sites of wind transported sediment strong control by bedrock topography means that the largest bedform wavelengths are not a result of particle trajectories and this complicates their comparison with other ripples and may require a new classification of relevance to mars the puna megaripples are morphologically and contextually similar to small ripple like transverse aeolian ridges tars moreover the puna gravels have similar equivalent weight mg to those composing granule ripples at meridiani planum and their local origin may have implications for the origin of sediment in martian aeolian bedforms finally the stable yet dynamic character of the puna megaripples could help reconcile current models of tars with periodic bedrock ridges that may be produced by aeolian erosion

the largest wind ripples on earth comment the dominance of aeolian features on the surface of mars requires a better understanding of potential terrestrial analogs to provide constraints on models of origin in his timely article milana 2009 1 describes the largest wind ripples on earth from the puna plateau of argentina inverting

ripple migration and dune activity on mars evidence for dynamic wind processes 1 in this report we show evidence of widespread ripple migration over the stoss side of dark barchan dunes in nili patera on mars the measured average migration of 1 7 meters in less than 4 terrestrial months clearly indicates that active sand saltation is occurring in the study area in addition we document widespread changes in the dune base ground surface contact and in the slip face structures showing that not only the ripples but the whole dunes are actually migrating in the present day atmospheric setting these results provide unequivocal evidence of recent aeolian activity and suggest that other dunes and ripples on mars may also be active

a theoretical model for aeolian impact ripples new insights into the grain bed impact process arising from both numerical and physical experiments involving single grain impacts lead to a more complete conceptual model of the aeolian saltation process that in turn allows a simple model of aeolian impact ripples to be developed the saltating population may be idealized as consisting of 1 long trajectory high impact energy constant impact angle successive saltations and 2 short trajectory low impact energy reptations it is argued that the spatial variations in mass flux due to the reptating population lead to the growth and translation of impact ripples using the sediment continuity equation an expression for the spatial variation in the ejection rate of reptating grains from a sinusoidally perturbed bed and a probability distribution for the reptation lengths a simple stability analysis demonstrates that the flat bed is unstable to small amplitude perturbations a fastest growing wavelength emerges that is roughly six times the mean reptation length and is only weakly dependent upon the detailed shape of the probability distribution of reptation lengths the results match well with the observed initial wavelengths in wind tunnel experiments

airflow reversal and alternating corkscrew vortices in foredune wake zones during perpendicular and oblique offshore winds on all sandy coastlines fringed by dunes understanding localised air flow allows us to examine the potential sand transfer between the beach and dunes by wind blown aeolian action traditional thinking into this phenomenon had previously included only onshore winds as effective drivers of this transfer recent research by the authors however has shown that offshore air flow too can contribute significantly through lee side back eddies to the overall windblown sediment budget to coastal dunes under rising sea levels and increased erosion scenarios this is an important process in any post storm recovery of sandy beaches until now though full visualisation in 3d of this newly recognised mechanism in offshore flows has not been achieved here we show for the first time this return flow eddy system using 3d computational fluid dynamics modelling and reveal the presence of complex corkscrew vortices and other phenomena the work highlights the importance of relatively small surface undulations in the dune crest which act to induce the spatial patterns of airflow and transport found on the adjacent beach

largest wind ripples on earth unique wind ripples attaining heights to 2 3 m wavelengths to 43 m and a crest maximum grain size of 19 mm occur on the argentine puna plateau at 4000 m altitude these are the largest ripples reported on earth comparable only to mars counterparts they form in the presence of high proportions of low density pumice clasts 0 91 g cm 3 although crests are exclusively composed of varnished normal density clasts 2 43 g cm 3 mature ripple profiles are partly excavated on bedrock so they form by a combination of deflation winnowing of finer grains minor wind drift of fine gravel and lagging of clasts 4 cm the large ripple size appears to be related to strong winds dense saltation layers and a long time for evolution ripple sizes are smaller on obstacles as compared to flat terrain there is a lack of correlation between clast size wavelength and the extreme ripple size in spite of the thin atmosphere all of which suggest that while small scale gravel ripples may form according to a reptation model their evolution into large scale types may relate to aerodynamic instabilities originating at the saltation curtain air interface

transverse aeolian ridges on mars first results from hirise images abstract three images obtained by the high resolution imaging science experiment hirise were analyzed for the information they could provide regarding transverse aeolian ridges tars on mars tars from five locations in a hirise image of the floor of ius chasma show remarkably symmetric cross sectional profiles with average slopes for the entire feature of 15 these results apply to tars that span an order of magnitude in wavelength and a factor of 6 in height a hirise image of gamboa impact crater in the northern lowlands shows low albedo sand patches

spatial grain size sorting in eolian ripples and estimation of wind conditions on planetary surfaces application to meridiani planum mars the landscape seen by the mars exploration rover mer opportunity at meridiani planum is dominated by eolian wind blown ripples with concentrated surface lags of hematitic spherules and fragments these ripples exhibit profound spatial grain size sorting with well sorted coarse grained crests and poorly sorted generally finer grained troughs these ripples were the most common bed form encountered by opportunity in its traverse from eagle crater to endurance crater field measurements from white sands national monument new mexico show that such coarse grained ripples form by the different transport modes of coarse and fine grain fractions on the basis of our field study and simple theoretical and experimental considerations we show how surface deposits of coarse grained ripples can be used to place tight constraints on formative wind conditions on planetary surfaces activation of meridiani planum coarse grained ripples requires a wind velocity of 70 m s at a reference elevation of 1 m above the bed from images by the mars orbiter camera moc of reversing dust streaks we estimate that modern surface winds reach a velocity of at least 40 m s and hence may occasionally activate these ripples the presence of hematite at meridiani planum is ultimately related to formation of concretions during aqueous diagenesis in groundwater environments however the eolian concentration of these durable particles may have led to the recognition from orbit of this environmentally significant landing site

periodic bedrock ridges on mars 1 evidence for sediment transport and erosion by wind is widespread over the surface of mars today and was likely a major geomorphic process for much of its geological past although martian surface features resembling aeolian dunes and ripples have been recognized since the mariner and viking missions such features have been interpreted previously as active indurated or exhumed sedimentary forms here we report evidence based on high resolution imaging science experiment images that show some megaripple forms are eroded into cohesive substrate rather than being composed of loose granular material or fossilized dunes exposure of stratigraphic continuity within layered cohesive material extending crest to trough through features with mean wavelengths of 18 to 51 m demonstrates the primarily erosional formation of what we term periodic bedrock ridges pbrs hence some surfaces on mars previously considered to be covered by wind deposited material are actually wind carved exposures that offer windows into martian history pbrs lack the distinctive streamlining associated with wind parallel yardangs and comparison of pbr orientation to yardangs megayardangs and active sedimentary dunes in the same vicinity confirm that these pbrs formed transverse to prevailing winds observed wavelengths of pbrs are comparable to those predicted by a simple model for erosional wavelengths of periodic transverse bed forms owing to the spacing of flow separations within the flow recognition of these transverse aeolian erosional forms brings up the question of how widespread martian pbrs are and how many have been misinterpreted as active or indurated fossilized sedimentary dunes