orbital observations of contemporary dune activity in endeavor crater meridiani planum mars 1 although aeolian landforms are pervasive on mars evidence for contemporary activity has been limited the next major campaign for the mars exploration rover opportunity is the investigation of the 20 km diameter endeavor crater 6 km to southeast of the rover s position as of december 2010 we present evidence from orbital imagery that eight aeolian bed forms 14 000 m2 in endeavor crater have been active within the past decade 2001 2009 at a spatial scale that should be directly observable by opportunity from the crater rim two dunes appear to show translational migration 10 20 m but all dunes indicate erosion to be the dominant process with up to 100 sediment removal thermophysical properties of these dunes are consistent with very fine to fine sand sizes the particle sizes most easily moved by the martian atmosphere the dunes that show the most surface change have a rippled appearance without well defined slip faces based on their morphology elliptical shape we classify them as dome dunes mesoscale atmospheric modeling is employed to provide insight into the atmospheric forcing of this aeolian system the major wind regimes from modeling are consistent with observations of wind streaks sand streamers ripples and slip faces of regional dune fields although modeled wind speeds are insufficient to move sand the translation and erosion of these dunes constitutes the largest contemporary movement of sand sized sediment reported on mars to date and demonstrates that endeavor crater has been subject to wind profiles exceeding the threshold velocity at the surface daily seasonally and or episodically in the recent past

orbital monitoring of martian surface changes abstract a history of martian surface changes is documented by a sequence of global mosaics made up of mars global surveyor mars orbiter camera daily color images from 1999 to 2006 together with a single mosaic from the mars reconnaissance orbiter mars color imager in 2009 these observations show that changes in the global albedo patterns of mars take place by a combination of dust storms and strong winds many of the observed surface changes took place along the tracks of seasonally repeating winter dust storms cataloged by wang and richardson 2015 these storms tend to sweep dust towards the equator progressively shifting albedo boundaries and continuing surface changes that began before the arrival of mgs the largest and most conspicuous changes took place during the global dust storm of 2001 my 25 which blanketed syrtis major stripped dust from the tharsis region and injected dust into solis planum high wind speeds but low wind stresses are predicted in syrtis tharsis and solis by the nasa ames gcm frequent changes in these regions show that dust accumulations are quickly removed by stronger winds that are not predicted by the gcm but may result from smaller scale influences such as unresolved topography

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

early views of the martian surface from the mars orbiter camera of mars global surveyor high resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms dunes sandsheets and drifts are prevalent and exhibit a range of morphology composition inferred from albedo and age as seen in occurrences of different dune orientations at the same location steep walls of topographic depressions such as canyons valleys and impact craters show the martian crust to be stratified at scales of a few tens of meters the south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non volatile components low resolution regional views of the planet provide synoptic observations of polar cap retreat condensate clouds and the lifecycle of local and regional dust storms

recent near surface wind directions inferred from mapping sand ripples on martian dunes abstract the high resolution imaging science experiment hirise provides the capability to obtain orbital images of mars that are of sufficient resolution to record wind ripple patterns on the surfaces of sand dunes ripple patterns provide valuable insights into aeolian erosion and deposition on earth and mars in this study we develop a systematic mapping procedure to examine sand ripple orientations and create surface process maps to evaluate the recent wind flow over the dunes as well as the interplay of wind and dune shape by carefully examining the morphology of the dunes and the location of grainflow and grainfall on dune slipfaces the recent near surface wind direction short term wind can be identified results from the analysis of three dune fields on the floors of craters west of hellas basin show regional n nw se and ese wind directions in the three adjacent dune fields surface process and flow maps suggest a complex wind pattern the comparison of short term wind with dune constructing wind long term wind shows ne and ese winds may be persistent at least for the past thousands of years the results also show that the orientation of inferred wind direction on linear dunes is correlated with the crestlines which suggest that form flow interaction may take place the results of local wind flow documentation should improve martian surface wind modeling and advance our understanding of sand transport as well as the rates of sand mobility on both mars and earth

dark aeolian sediments in martian craters composition and sources our research focuses on the mineralogical characteristics of dark sediment deposits in martian craters dunes dune fields and sand sheets and their local sediment sources carried out on the basis of 70 selected localities morphological analyses reveal dark layers exposed in a number of crater walls showing indications of material transport from the layers downwall to the intracrater deposits additional sites show dark sediment emerging from several craters floors suggesting a dark material source beneath the crater floor spectral analyses of omega and crism data showed for the first time that a direct mineralogical connection exists between the dark layers in the crater walls and the intracrater dune and sand sheet material based on these findings it is shown that these layers are the local sources for the dark aeolian sediment inside the craters spectral analyses further indicate that all deposits are nearly of the same mafic mineralogical composition hinting at a similar origin we conclude that the mineralogical composition points to a volcanic origin of the material the dark layers which we infer to be the material sources might represent layers of volcanic ash almost globally deposited in early noachian times and subsequently covered by regolith groundwater impact erosion and crustal movement led to the highly fragmented situation of the dark layers today however burial protected the layers of dark sediment from chemical alteration caused by surficial fluvial processes impact erosion after the wet periods on mars led to the exposure and mobilization of the material today

martian surface winds insensitivity to orbital changes and implications for aeolian processes aeolian features observed on the surface of mars provide insight into current and potentially past surface wind systems in some cases the features are clearly transient and related to the lifting and settling of atmospheric dust other features like dunefields yardangs and ventifacts are more persistent and likely require significant time to form in this study we analyze the observed directions of selected aeolian features with the aid of the geophysical fluid dynamics laboratory mars general circulation model gcm initially we examine bright and dark streaks which have been observed to form in association with global dust storms the ability to match these features with mars gcm wind directions provides an important validation of the model more important we are able to define best fit seasons and local times for both types of features which provide the basis for extension and modification of the veverka et al 1981 model of bright and dark dust streak formation in addition these best fit times correspond well with the dark streak wind storm model of magalhaes and young 1995 the primary focus of this paper is to provide constraints on the range of mechanisms proposed to explain inconsistencies between current wind direction patterns and long term wind indicators for example the misalignment of rock tail and ventifact orientations at the mars pathfinder landing site specifically we assess whether changes in planetary obliquity precession or global dust opacity could significantly alter patterns of surface wind directions in all cases we find the seasonal and annual average wind direction patterns to be highly invariable while changes in the dust loading hence the partitioning of solar absorption between the surface and atmosphere and in the surface latitude of maximum solstitial insolation cause the vigor of the large scale circulation to increase especially the hadley cell the spatial patterns of the surface wind orientations remain essentially unchanged in the case of perihelion during northern summer opposite of the current perihelion position the northern summer hadley cell remains weaker than the southern summer cell despite the strengthened heating in the northern hemisphere taken together these results cast significant doubt on orbital explanations for surface wind changes it is thus suggested that significant changes in topography e g tharsis uplift true polar wander or climate e g the existence of a significantly thicker atmosphere or an ocean at some point in the past are more likely explanations for long term wind indicators such as the ventifact orientations at the mars pathfinder landing site

inverse maximum gross bedform normal transport 2 application to a dune field in ganges chasma mars and comparison with hirise repeat imagery and mrams abstract inverse maximum gross bedform normal transport imgbnt analysis has been applied to context camera ctx images of the largest dune field in ganges chasma on mars the dune field was selected for its position in a likely complex multi directional wind regime results indicate that four main winds are responsible for simultaneous construction of the dune field including along chasma winds from the ese winds blowing down a nearby re entrant from the ne winds blowing down the adjacent chasma wall from the nw and chasma floor winds from the sw each wind represents a transport vector that dominates dune morphology at its respective edge of the dune field such that the central axis of the dune field reflects the convergence of the three most prominent winds ese nw and sw the mars regional atmospheric modeling system mrams was run at twelve times throughout the martian year to provide context for the local wind patterns potential sand fluxes calculated from mrams output show that three major air flows from the ene e nne ne and nnw n converge near the location of the dune field these flows likely correspond to the ese ne and nw winds identified from imgbnt analysis respectively mrams output shows that the flows with major northerly components are produced by larger scale hadley return flow constructively combining with nighttime downslope winds the flow with a major easterly component is likely produced by equatorial easterly trade winds constructively combining with the diurnal tide and or local topography although the model correctly predicts the major elements of the local wind pattern some aspects are either over or underrepresented demonstrating the value of using aeolian morphological analysis to conclusively constrain the major sand moving winds on mars overlapping high resolution imaging experiment hirise images of barchanoid dunes at the northernmost edge of the dune field indicate that these dunes are currently migrating southward at 5 m mars year 2 6 m earth year the direction of migration is consistent with both mrams predictions in this location and the nw ne winds found from imgbnt analysis dune morphology suggests that sand in the northwestern part of the dune field is likely to be derived from the adjacent chasma wall to the north and northwest and sand in the southeastern part of the dune field was probably transported from farther east along the main chasma floor

observations of an aeolian landscape from surface to orbit in gale crater abstract landscapes derived solely from aeolian processes are rare on earth because of the dominance of subaqueous processes in contrast aeolian derived landscapes should typify mars because of the absence of liquid water the long exposure times of surfaces and the presence of wind as the default geomorphic agent using the full range of available orbital and mars science laboratory rover curiosity images wind formed features in gale crater were cataloged and analyzed in order to characterize the aeolian landscape and to derive the evolution of the crater wind regime over time inferred wind directions show a dominance of regional northerly winds over geologic time scales but a dominance of topography driven katabatic winds in modern times landscapes in gale crater show a preponderance of aeolian features at all spatial scales interpreted processes forming these features include first cycle aeolian abrasion of bedrock pervasive deflation organization of available sand into bedforms abundant cratering and gravity driven wasting all of which occur over a background of slow physical weathering the observed landscapes are proposed to represent a spectrum of progressive surface denudation from fractured bedrock to retreating bedrock capped mesas to remnant hills capped by bedrock rubble to desert pavement plains this model of landscape evolution provides the mechanism by which northerly winds acting over 3 ga excavated tens of thousands of cubic kilometers of material from the once sediment filled crater thus carving the intra crater moat and exhuming mount sharp aeolis mons the current crater surface is relatively sand starved indicating that potential sediment deflation from the crater is greater than sediment production and that most exhumation of mount sharp occurred in the ancient geologic past

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

dune morphology sand transport pathways and possible source areas in east thaumasia region mars an aeolian system located in aonia terra eastern thaumasia region consists of six dark dune fields the dune pattern suggests an organized extended sand transport system which is characterized by the presence of long sand corridors the latter connects the different ergs with potential sources the sand stored in the ergs is provided by layered materials exposed in pits and crater walls and by the ergs themselves most of the sand converges from the marginal dune fields into the central erg c the latter develops in an area of convergence of at least three different winds from the southwest the northeast and the northwest the northwesterly flows seem to postdate the other winds as suggested by the development of a complex dune pattern in the western portion of the erg c representing a successive episode of aeolian construction collectively such complex dune patterns show how dune fields could record major changes in the wind regimes of mars

occurrence and scale of compositional heterogeneity in martian dune fields toward understanding the effects of aeolian sorting on martian sediment compositions abstract aeolian transport and hydrodynamic sorting have been proposed to be a significant influence on martian sediment bulk compositions through laboratory experiments modeling and terrestrial analogies but to date few studies have directly examined compositional grain size relationships within sediment fields on mars thus the prevalence of hydrodynamic sorting as well as the scales at which sorting is important remain poorly understood to that end we assessed the degree and occurrence of thermophysical and compositional heterogeneity for 25 dune fields within a 42 000 000 km2 area on mars among these only four exhibit spatial heterogeneity in spectral properties and composition two of these four sites show a strong positive relationship between particle size and olivine abundance the rarity of compositional heterogeneity within dune fields in our study region 5 185 e 45 n 20 s may indicate phenocryst poor source rocks alternatively sorting within individual bedforms may be present but not at the scale of the full dune field 10 20 km compositional segregation correlated with grain size due to hydrodynamic sorting has been observed by rovers at scales much smaller than themis ground resolution 100 m pixel thus these small scales might be the operable relevant ones of hydrodynamic compositional sorting prevailing most commonly in martian dune fields

the influence of local topography for wind direction on mars two examples of dune fields in crater basins in this work we perform an analysis of large dark dunes within moreux crater and herschel crater on mars using high resolution imaging science experiment hirise and context camera ctx data sets these data allow us to conduct a detailed analysis of dune morphology and slip faces concluding that the studied dune fields are influenced by topographically controlled complex wind directions our morphological analysis reveals that inside moreux crater in particular the topographic setting dominates the wind flow direction leading to the development of a sand transport pathway encircling the central peak of the crater the dune fields in herschel crater are also affected by winds controlled by variable topography as suggested by the presence of complex dunes and dune fields our analysis indicate that the studied dune systems is not the result of paleo wind regimes furthermore we perform thermal inertia measurements using thermal emission spectrometer tes data which indicate that the studied dune fields consist of medium sand 250 500 mm in diameter

changes in blast zone albedo patterns around new martian impact craters abstract blast zones bzs around new martian craters comprise various albedo features caused by the initial impact including diffuse halos extended linear and arcuate rays secondary craters ejecta patterns and dust avalanches we examined these features for changes in repeat images separated by up to four mars years here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time such changes are most likely due to airfall of high albedo dust restoring darkened areas to their original albedo the albedo of adjacent non impacted surfaces although some sites show drastic changes over short timescales nearly half of the sites show no obvious changes over several mars years albedo changes are more likely to occur at higher latitude sites lower elevation sites and at sites with smaller central craters no correlation was seen between amount of change and dust cover index relative halo size or historical regional albedo changes quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features the average lifetime among sites with measurable fading is 15 mars years the median is 8 mars years for a linear brightening however at approximately half of sites with three or more repeat images a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior this would predict even longer lifetimes the predicted lifetimes of bzs are comparable to those of slope streaks and considered representative of fading by global atmospheric dust deposition they last significantly longer than dust devil or rover tracks albedo features that are erased by different processes these relatively long lifetimes indicate that the measurement of the current impact rate by daubar et al daubar i j et al 2013 icarus 225 506 516 http dx doi org 10 1016 j icarus 2013 04 009 does not suffer significantly from overall under sampling due to blast zones fading before new impact sites can be initially discovered however the prevalence of changes seen around smaller craters may explain in part their shallower size frequency distribution

flume experiments on the alignment of transverse oblique and longitudinal dunes in directionally varying flows for more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow whereas others are parallel or oblique to flow this problem of bedform alignment was studied experimentally using subaqueous dunes on a 3 6 m diameter sand covered turntable on the floor of a 4 m wide flume in each experiment two flow directions relative to the bed were produced by alternating the turntable between two orientations the turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms the resulting bedforms were in equilibrium with the time averaged conditions of the bimodal flows dune alignment was studied for five divergence angles the angle between the two flow directions 45 67 5 90 112 5 and 135 the flow depth during all experiments was approximately 30 cm mean velocity was approximately 50 cm s 1 and mean grain diameter was 0 6 mm each experiment continued for 30 75 min during which time the flume flow was steady and the turntable position changed every 2 min at the end of each experiment water was slowly drained from the flume and dune alignment was measured transverse dunes defined relative to the resultant transport direction were created when the divergence angle was 45 and 67 5 and longitudinal dunes were created when the divergence angle was 135 at intermediate divergence angles dunes with both orientations were produced but transverse dunes were dominant at 90 and longitudinal dunes were dominant at 112 5 one experiment was conducted with a divergence angle of 135 and with unequal amounts of transport in the two flow directions this was achieved by changing the orientation of the turntable at unequal time intervals thereby causing the amount of transport to be unequal in the two directions the dunes formed during this experiment were oblique to the resultant transport direction these experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments in both sets of experiments the bedforms developed with the orientation having the maximum gross bedform normal transport the orientation at which the sum of the bedform normal components of the two transport vectors reaches its maximum value in other words the bedforms develop with an orientation that is as transverse as possible to the two flows in those cases where the two flows diverge by more than 90 and transport equal amounts of sand bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors although such bedforms have been defined by previous work as longitudinal bedforms they are intrinsically the same kind of bedform as transverse bedforms

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

first in situ investigation of a dark wind streak on mars 1 prominent low albedo wind streaks issue from embayments at the north end of victoria crater in meridiani planum the site of surface investigations by the mars exploration rover opportunity opportunity was sent to examine the darkest of these wind streaks and compare it to the adjacent soil in the brighter corridor between the streaks two nearby sites inside and outside of the streak were selected for visible and infrared remote sensing and for elemental abundance measurements and images of the microscopic soil morphology the rover was next sent to study the interaction of the wind streak with an obstacle a small rock near the source of the streak opportunity s observations suggest that the victoria wind streaks are deposits of basaltic sand blown out of the crater from the dark dunes nestled below the crater rim particularly at the base of the alcove leading up to the darkest streak no local sources of sand have been identified within the victoria crater wall rock suggesting that the sand is supplied from outside the crater and is presently escaping its temporary topographic trap this process presents a possible explanation for the serrated margin of victoria crater through abrasion of the soft rock as trapped sands are blown out of the crater and carve alcoves under various seasonal winds some indication of the rate of activity of these wind streaks will be provided by continued monitoring of the erasure of the rover s tracks

craters as sand traps dynamics history and morphology of modern sand transport in an active martian dune field abstract aeolian transport of sand is abundant on modern day mars as revealed by remote sensing measurements of the motion of dunes and of the meter scale ripples that mantle them we study a large scale natural sand trap within the meroe patera dune field a 1 8 km diameter crater which features a dune free shadow in its lee we compare the volume of sand trapped within this crater to the sand volume that would be expected to cover the area of the crater and its dune free shadow behind it if the crater were not present we find that the crater holds less sand than this missing volume would predict implying that sand escapes from the crater over time modern day imagery shows an apparent lack of sand escaping from the meroe crater however suggesting that changes in the wind regime at the site may have allowed sand to escape in the past the persistence of an altered dune morphology all the way to the far downwind edge of the dune field suggests consistent wind conditions over the time of the crater dune field interaction

updating the global inventory of dune fields on mars and identification of many small dune fields abstract the mars global digital dune database mgd3 archives the location of large dark dunes on mars including several morphological mineralogical and thermophysical characteristics it has been widely used by the mars scientific community as a resource for aeolian studies hayward r k mullins k f fenton l k hare t m titus t n bourke m c colaprete a and christensen p r 2007a mars global digital dune database mc2 mc29 u s geological survey open file report 2007 1158 doi https doi org 10 3133 20071158 this work presents the results of a new global dune field survey using high resolution orbital images of mars that have been acquired in the years since the mgd3 was first compiled more than 2000 new dune fields have been identified and mapped more than doubling the previous number known the new dune fields are mostly small

dust production by abrasion of eolian basalt sands analogue for martian dust dust is nearly ubiquitous on mars covering much of the planet s surface having been redistributed by dust storms analysis of dust via landed instrumentation indicates a basaltic composition for its protolith the same is interpreted for the dark dune sands encountered at rover field sites in this paper we used samples of aeolian sands derived from basaltic volcanoes in an experiment to simulate dust production from basalt dune sands within an abrasion chamber in addition we used samples from gypsum dunes because gypsum is found within dune fields on the northern plains of mars the results expressed as weight of sample reduced to dust show a remarkably broad range over four orders of magnitude aeolian abrasion of basalt sands can produce similar amounts of dust as is the case for some desert sands on earth some plausible mars analogue materials can produce large amounts of dust suggesting that aeolian movement of basaltic sand and volcanic sediments on the surface of mars is a potential source of fine grained sediment or dust

mars landscape evolution influence of stratigraphy on geomorphology in the north polar region abstract lithology and physical properties of strata exposed at the earth s surface have direct influence on the erosion and geomorphic expression of landforms while this is well known on our planet examples on mars are just coming to light among the tens of thousands of airphoto quality images resolutions 1 5 12 m pixel acquired since 1997 by the mars global surveyor mgs mars orbiter camera moc specific examples occur among martian north polar layered materials which moc images reveal are divided into two distinct stratigraphic units a lower dark toned layered unit and a younger upper lighter toned layered unit the lower unit is less resistant to wind erosion than the upper unit the upper unit most likely consists of stratified dust and ice while the lower unit contains abundant poorly cemented sand sand is more easily mobilized by wind than dust the lower resistance to erosion of the lower unit results from the presence of sand where wind erosion in polar troughs has penetrated to the lower unit geomorphic change has proceeded more rapidly sand has been liberated from the lower unit and arcuate scarps have formed as the upper unit has been undermined wind erosion of the lower unit thus influences the geomorphology of the north polar region this result likely explains the genesis of the large polar trough chasma boreale and the relations between dunes and arcuate scarps that have puzzled investigators for nearly three decades the properties of the stratigraphic units suggest that the upper limit for the amount of water contained in the north polar layered materials may be 30 50 less than previously estimated

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 dunes as ground truth for atmospheric modeling on mars 1 martian aeolian dunes preserve a record of atmosphere surface interaction on a variety of scales serving as ground truth for both global climate models gcms and mesoscale climate models such as the mars regional atmospheric modeling system mrams we hypothesize that the location of dune fields expressed globally by geographic distribution and locally by dune centroid azimuth dca may record the long term integration of atmospheric activity across a broad area preserving gcm scale atmospheric trends in contrast individual dune morphology as expressed in slipface orientation sf may be more sensitive to localized variations in circulation preserving topographically controlled mesoscale trends we test this hypothesis by comparing the geographic distribution dca and sf of dunes with output from the ames mars gcm and at a local study site with output from mrams when compared to the gcm 1 dunes generally lie adjacent to areas with strongest winds 2 dca agrees fairly well with gcm modeled wind directions in smooth floored craters and 3 sf does not agree well with gcm modeled wind directions when compared to mrams modeled winds at our study site 1 dca generally coincides with the part of the crater where modeled mean winds are weak and 2 sfs are consistent with some weak topographically influenced modeled winds we conclude that 1 geographic distribution may be valuable as ground truth for gcms 2 dca may be useful as ground truth for both gcm and mesoscale models and 3 sf may be useful as ground truth for mesoscale models

morphology development and sediment dynamics of elongating linear dunes on mars linear dunes occur on planetary surfaces including earth mars and titan yet their dynamics are poorly understood recent studies of terrestrial linear dunes suggest they migrate by elongation only in supply limited environments here we investigate elongating linear dunes in the hellespontus montes region of mars which are morphologically similar to terrestrial systems multi temporal high resolution orbital images show these linear dunes migrate by elongation only and that the fixed sediment source of the dunes probably restricts any lateral migration some linear dunes maintain their along length volume and elongate at rates comparable to adjacent barchans whereas those which decrease in volume show no elongation suggesting they are near steady state matching morphometric predictions limited sediment supply may restrict martian linear dunes to several kilometres significantly shorter than many terrestrial linear dunes our results demonstrate the close similarities in dune dynamics across the two planetary surfaces

recent aeolian dune change on mars previous comparisons of martian aeolian dunes in satellite images have not detected any change in dune form or position here we show dome dunes in the north polar region that shrank and then disappeared over a period of 3 04 mars years 5 7 earth years while larger neighboring dunes showed no erosion or movement the removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on mars but that any sand that is available for transport is likely to be moved dunes that show no evidence of change could be crusted indurated or subject to infrequent episodes of movement

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

aeolian sediment transport pathways and aerodynamics at troughs on mars 1 interaction between wind regimes and topography can give rise to complex suites of aeolian landforms this paper considers aeolian sediment associated with troughs on mars and identifies a wider range of deposit types than has previously been documented these include wind streaks falling dunes lateral dunes barchan dunes linear dunes transverse ridges sand ramps climbing dunes sand streamers and sand patches the sediment incorporated into these deposits is supplied by wind streaks and ambient planitia sources as well as originating within the trough itself notably from the trough walls and floor there is also transmission of sediment between dunes the flow dynamics which account for the distribution of aeolian sediment have been modeled using two dimensional computational fluid dynamics the model predicts flow separation on the upwind side of the trough followed by reattachment and acceleration at the downwind margin the inferred patterns of sediment transport compare well with the distribution of aeolian forms model data indicate an increase of wind velocity by 30 at the downwind trough margin this suggests that the threshold wind speed necessary for sand mobilization on mars will be more frequently met in these inclined locations

global map of eolian features on mars ten basic categories of eolian features on mars were identified from a survey of mariner 9 and viking orbiter images the ten features mapped are 1 light streaks including frost streaks 2 dark streaks 3 sand sheets or splotches 4 barchari dunes 5 transverse dunes 6 crescentic dunes 7 anomalous dunes 8 yardangs 9 wind grooves and 10 deflation pits the features were mapped in groups not as individual landforms and recorded according to their geographic positions and orientations on maps of 1 12 5 million or 1 25 million scale in the north polar region light and dark streaks indicate winds from the west and northwest frost streaks show northeast and northwest winds barchan dunes show southwest and west winds transverse dunes show east and west winds local erosional features show winds from the northwest or southeast and northeast or southwest in the middle and low northern latitudes streaks show northeast winds yardangs and deflation pits show mostly easterly and northeasterly winds in the low southern latitudes light streaks and dunes record northwest and northeast winds dark streaks record southeast winds in high southern latitudes most streaks and dunes record southeast and east winds in the south polar region light and frost streaks record southwest and northwest winds whereas dark streaks and transverse dunes show southeast winds the patterns recorded for ephemeral features conform to global conditions of strong southern spring and summer northern fall and winter wind circulation erosional features in bedrock indicate long term and perhaps ancient wind trends whereas depositional features may record relatively more recent winds wind directions indicated by yardangs pits and other erosional features seldom correspond to those shown by streaks these erosional features indicating winds of different directions than those that formed the streaks may have been carved when the effective regional winds on mars were different due to relative hemisphere insolation differences which are related to obliquity variations alternatively many yardangs and pits may be largely controlled by structure and carved along surface structural patterns or features that channeled both ancient and present day winds deflation pits in the mantled terrain may contain the best record of ancient wind trends these pits seem to have stratigraphically related orientations different stratigraphic units composing the mantle contain wind erosion pits that possibly record large scale wind direction changes because of long term changes in the obliquity of the mars

mars global digital dune database mgd 3 global dune distribution and wind pattern observations abstract the mars global digital dune database mgd 3 is complete and now extends from 90 n to 90 s latitude the recently released south pole sp portion mc 30 of mgd 3 adds 60 000 km 2 of medium to large size dark dune fields and 15 000 km 2 of sand deposits and smaller dune fields to the previously released equatorial eq 70 000 km 2 and north pole np 845 000 km 2 portions of the database bringing the global total to 975 000 km 2 nearly all np dunes are part of large sand seas while the majority of eq and sp dune fields are individual dune fields located in craters despite the differences between mars and earth their dune and dune field morphologies are strikingly similar bullseye dune fields named for their concentric ring pattern are the exception possibly owing their distinctive appearance to winds that are unique to the crater environment ground based wind directions are derived from slipface sf orientation and dune centroid azimuth dca a measure of the relative location of a dune field inside a crater sf and dca often preserve evidence of different wind directions suggesting the importance of local topographically influenced winds in general however ground based wind directions are broadly consistent with expected global patterns such as polar easterlies intriguingly between 40 s and 80 s latitude both sf and dca preserve their strongest though different dominant wind direction with transport toward the west and east for sf derived winds and toward the north and west for dca derived winds

dune migration and slip face advancement in the rabe crater dune field mars 1 eight overlapping images of a dune slip face in rabe crater 35 e 44 s from the mars global surveyor mars orbiter camera show changes interpreted to be multiple grainflow events that would indicate present day sand saltation and dune migration new occurrences of these features appear sporadically throughout late southern summer and early fall and then no further changes occur throughout winter by the following summer the pattern of old streaks had been almost completely covered by new dark streaks assuming that this activity is typical from year to year migration rates are estimated to be on the order of 1 2 cm per martian year produced by south to southeasterly winds that blow mostly during the southern spring and early summer this slow migration rate is consistent with a present day sediment state that is either transport or availability limited

earth aeolian wind streaks comparison to wind data from model and stations wind streak is a collective term for a variety of aeolian features that display distinctive albedo surface patterns wind streaks have been used to map near surface winds and to estimate atmospheric circulation patterns on mars and venus however because wind streaks have been studied mostly on mars and venus much of the knowledge regarding the mechanism and time frame of their formation and their relationship to the atmospheric circulation cannot be verified this study aims to validate previous studies results by a comparison of real and modeled wind data with wind streak orientations as measured from remote sensing images orientations of earth wind streaks were statistically correlated to resultant drift direction rdd values calculated from reanalysis and wind data from 621 weather stations the results showed good agreement between wind streak orientations and reanalysis rdd r 0 78 a moderate correlation was found between the wind streak orientations and the weather station data r 0 47 a similar trend was revealed on a regional scale when the analysis was performed by continent with r ranging from 0 641 in north america to 0 922 in antarctica at sites where wind streak orientations did not correspond to the rdds i e a difference of 45 seasonal and diurnal variations in the wind flow were found to be responsible for deviation from the global pattern the study thus confirms that earth wind streaks were formed by the present wind regime and they are indeed indicative of the long term prevailing wind direction on global and regional scales

barchan dune asymmetry observations from mars and earth barchan dune asymmetry refers to the extension of one barchan limb downwind it is a common dune form on earth and also occurs on mars and titan a new classification of barchan limbs is presented where three types of limb morphology are identified linear kinked and beaded these along with other dune scale morphological signatures are used to identify three of the causes of barchan asymmetry on mars bi directional winds dune collision and the influence of inclined topography the potential for specific dune asymmetric morphologies to indicate aspects of the formative wind regime on planetary surfaces is shown for example the placement of dune limbs can indicate the general direction and relative strength of formative oblique winds an extreme barchan limb length may indicate a long duration oblique wind a kinked limb may be evidence of the passage of a storm beaded limbs may represent surface wave instabilities caused by an increase in wind energy parallel to the dune a preliminary application of these signatures finds evidence for bi modal winds on mars however these and other morphological signatures of wind direction and relative strength should be applied to planetary landforms with caution as more than one process e g bi modal winds and collision may be operating together or sequentially on the dunefield in addition analysis should be undertaken at the dunefield scale and not on individual dunes finally morphological data should be acquired from similar scale dunes within a dunefield in addition to bi modal wind regimes on mars the frequent parallel alignment of the extended barchan limb to the dune suggests that dune collision is also an important cause of asymmetry on mars some of the more complex dunefield patterns result from a combination of dune collision limb extension and merging with downwind dunes dune asymmetric form does not inhibit dune migration in the namib desert or on mars data from the namib suggest that dune migration rates are similar for symmetric and asymmetric dunes further modeling and field studies are needed to refine our understanding of the potential range of limb and dune morphologies that can result from specific asymmetry causes

sediment volume in the north polar sand seas of mars data from studies of the cross sectional area of terrestrial transverse dunes have been combined with maps of dune morphometry derived from viking orbiter images to generate new estimates of sediment thickness and dune sediment volume in the north polar sand seas of mars a relationship between dune spacing and equivalent sediment thickness est was developed from field data on namibian and north american dunes and was applied to data on dune spacing and dune cover measured on viking orbiter images to generate maps of dune sediment thickness for martian north polar sand seas there are four major sand seas in the north polar region of mars covering an area of 6 8 105 km2 equivalent sediment thickness ranges between 0 5 and 6 1 m with a mean of 1 8 m the sand seas contain a total of 1158 km3 of dune sediment which may have been derived by erosion of polar layered deposits and concentrated in its present location by winds that change direction seasonally

object based dune analysis automated dune mapping and pattern characterization for ganges chasma and gale crater mars abstract a method that enables the automated mapping and characterization of dune fields on mars is described using ctx image mosaics the introduced object based dune analysis obda technique produces an objective and reproducible mapping of dune morphologies over extensive areas the data set thus obtained integrates a large variety of data allowing a simple cross analysis of dune patterns spectral and morphometric information and mesoscale wind models two dune fields located in gale crater and ganges chasma were used to test and validate the methodology the segmentation of dune related morphologies is highly efficient reaching overall accuracies of 95 in addition we show that the automated segmentation of slipface traces is also possible with expected accuracies of 85 90 a qualitative and quantitative comparison of the final outputs with photointerpretations is performed and the precision of the directional characterization of the dune patterns is evaluated we demonstrate a good agreement between the obda outputs and the photointerpreted dune morphologies with local trend deviations below 45 for 80 95 of the mapped areas because the developed algorithm is tuned for the recognition of linear features from the imagery the slipfaces of small barchans can be preferentially overlooked owing to their small extent at the spatial resolution of the ctx mosaics dune types composed of longer linear morphologies are much better represented including correct mapping of secondary structures having proved the effectiveness and accuracy of the mapping procedure we discuss its future applications for the improvement of dune catalogs on mars

an aeolian grainflow model for martian recurring slope lineae abstract recurring slope lineae rsl on mars have been enigmatic since their discovery their behavior resembles a seeping liquid but sources of water remain puzzling this work demonstrates that the properties of rsl are consistent with observed behaviors of martian and terrestrial aeolian processes specifically rsl are well explained as flows of sand that remove a thin coating of dust observed rsl properties are supportive of or consistent with this model which requires no liquid water or other exotic processes but rather indicates seasonal aeolian behavior these settings and behaviors resemble features observed by rovers and also explain the occurrence of many slope lineae on mars that do not meet the strict definition of rsl this indicates that rsl can be explained simply as aeolian features other processes may add complexities just as they could modify the behavior of any sand dune

dune field pattern formation and recent transporting winds in the olympia undae dune field north polar region of mars high resolution imaging science experiment hirise imagery of the central olympia undae dune field in the north polar region of mars shows a reticulate dune pattern consisting of two sets of nearly orthogonal dune crestlines with apparent slipfaces on the primary crests ubiquitous wind ripples areas of coarse grained wind ripples and deflated interdune areas geomorphic evidence and dune field pattern analysis of dune crest length spacing defect density and orientation indicates that the pattern is complex representing two constructional generations of dunes the oldest and best organized generation forms the primary crestlines and is transverse to circumpolar easterly winds gross bed form normal analysis of the younger pattern of crestlines indicates that it emerged with both circumpolar easterly winds and ne winds and is reworking the older pattern mapping of secondary flow fields over the dunes indicates that the most recent transporting winds were from the ne the younger pattern appears to represent an influx of sediment to the dune field associated with the development of the olympia cavi reentrant with ne katabatic winds channeling through the reentrant a model of the pattern reformation based upon the reconstructed primary winds and resulting secondary flow fields shows that the development of the secondary pattern is controlled by the boundary condition of the older dune topography

early mesozoic tectonic settings of the northern north china craton abstract this paper aims to reconstruct early mesozoic tectonic settings of the northern north china craton based on investigations of triassic middle jurassic successions and age determinations of some lithostratigraphic units and dikes cutting tilted early mesozoic strata it used to be regarded that the northern north china craton experienced fold thrust deformations in the triassic to early jurassic based on the occurrences of unconformity beneath triassic lower jurassic units synorogenic conglomerate and late triassic thrusting we revisited early mesozoic stratigraphy of the xiabancheng basin in the middle yanshan belt to restore tectonic environments during that period of time detrital zircon data reveal that the liujiagou and ermaying formations are actually of middle and late triassic ages respectively field observations show that the ermaying and xingshikou formations are conformable making up a sequence from fluvial to alluvial fan facies it is also noticeable that lower middle jurassic xingshikou through xiahuayuan succession is typified by fining and deepening upward depositional trend and contains abundant volcaniclastic rocks indicative of continued subsidence of the xiabancheng basin in a volcanic setting all the results cast doubts on the long held view that the first phase of shortening in the northern north china craton happened in the late triassic or early jurassic the angular unconformity beneath upper jurassic tiaojishan volcanics registered shortening in the northern north china craton which plausibly took place around 170 ma on account of zircon u pb ages of two dikes penetrating deformed middle triassic lower jurassic strata and ages of tiaojishan volcanics above the unconformity given the widespread occurrence of magmatism rift basins and metamorphic core complexes during the triassic and early jurassic it follows that the northern north china craton was more likely under an extensional setting during the early mesozoic

southern high latitude dune fields on mars morphology aeolian inactivity and climate change in a study area spanning the martian surface poleward of 50 s 1190 dune fields have been identified mapped and categorized based on dune field morphology dune fields in the study area span 116 400 km2 leading to a global dune field coverage estimate of 904 000 km2 far less than that found on earth based on distinct morphological features the dune fields were grouped into six different classes that vary in interpreted aeolian activity level from potentially active to relatively inactive and eroding the six dune field classes occur in specific latitude zones with a sequence of reduced activity and degradation progressing poleward in particular the first signs of stabilization appear at 60 s which broadly corresponds to the edge of high concentrations of water equivalent hydrogen content observed by the neutron spectrometer that have been interpreted as ground ice this near surface ground ice likely acts to reduce sand availability in the present climate state on mars stabilizing high latitude dunes and allowing erosional processes to change their morphology as a result climatic changes in the content of near surface ground ice are likely to influence the level of dune activity spatial variation of dune field classes with longitude is significant suggesting that local conditions play a major role in determining dune field activity level dune fields on the south polar layered terrain for example appear either potentially active or inactive indicating that at least two generations of dune building have occurred on this surface many dune fields show signs of degradation mixed with crisp brinked dunes also suggesting that more than one generation of dune building has occurred since they originally formed dune fields superposed on early and late amazonian surfaces provide potential upper age limits of 100 my on the south polar layered deposits and 3 ga elsewhere at high latitudes no craters are present on any identifiable dune fields which can provide a lower age limit through crater counting assuming all relatively stabilized dune fields represent a single noncontiguous surface of uniform age their estimated crater retention age is 10 000 years an average sized uncratered dune field 94 km2 has a crater retention age 8 my this apparent youth suggests that present day climate conditions are responsible for the observed degradation and reduced level of aeolian activity a lack of observed transport pathways and the absence of large dune fields in the largest basins hellas and argyre planitiae are consistent with the previously proposed idea that dune sands are not typically transported far from their source regions on mars

giant saltation on mars saltation the motion of sand grains in a sequence of ballistic trajectories close to the ground is a major factor for surface erosion dune formation and triggering of dust storms on mars although this mode of sand transport has been matter of research for decades through both simulations and wind tunnel experiments under earth and mars conditions it has not been possible to provide accurate measurements of particle trajectories in fully developed turbulent flow here we calculate the motion of saltating grains by directly solving the turbulent wind field and its interaction with the particles our calculations show that the minimal wind velocity required to sustain saltation on mars may be surprisingly lower than the aerodynamic minimal threshold measurable in wind tunnels indeed mars grains saltate in 100 times higher and longer trajectories and reach 5 10 times higher velocities than earth grains do on the basis of our results we arrive at general expressions that can be applied to calculate the length and height of saltation trajectories and the flux of grains in saltation under various physical conditions when the wind velocity is close to the minimal threshold for saltation

aeolian system sediment state theory and mojave desert kelso dune field example the sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply sediment availability and the transport capacity of the wind the sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system numerous factors impact the susceptibility of grains on a surface to transport but these are cumulatively manifested by the actual transport rate which serves as a proxy for sediment availability transport capacity is the potential sediment transport rate of the wind because the three aspects of sediment state can be given as a volumetric rate they are directly comparable plotted simultaneously against time the generated curves define nine possible classes of sediment state sediment supply that is stored occurs because it is transport or availability limited or generated at a rate greater than the potential or actual transport rates respectively contemporaneous or lagged influx to an aeolian system may be limited by sediment availability but cannot exceed the transport capacity of the wind for the kelso dune field in the mojave desert of california a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system the sediment supply was generated during the latest pleistocene and earliest holocene during humid periods of enhanced discharge by the mojave river to form the lake mojave fan delta or terminal fan and has been calculated over time from the sedimentation rate and the frequency of floods estimation of transport capacity over time was based upon modern wind data with an allowance for greater winds during the pleistocene based upon climatic models sediment availability was approximated by calculation of a modern dune mobility index with variation over time based upon climatic inferences while quantifying the kelso or any natural system is subject to numerous uncertainties the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at kelso as well as illuminating questions for future research

first quantification of relationship between dune orientation and sediment availability olympia undae mars abstract dunes provide unique information about wind regimes on planetary bodies where there is no direct meteorological data at the eastern margin of olympia undae on mars dune orientation is measured from satellite imagery and sediment cover is estimated using the high contrast between the dune material and substrate the analysis of these data provide the first quantification of relationship between sediment availability and dune orientation abrupt and smooth dune reorientations are associated with inward and outward dynamics of dunes approaching and ejecting from major sedimentary bodies respectively these reorientation patterns along sediment transport pathways are interpreted using a new generation dune model based on the coexistence of two dune growth mechanisms this model also permits solving of the inverse problem of predicting the wind regime from dune orientation for bidirectional wind regimes solutions of this inverse problem show substantial differences in the distributions of sediment flux orientation which can be attributed to atmospheric flow variations induced by changes in albedo at the boundaries of major dune fields then we conclude that relationships between sediment cover and dune orientation can be used to constrain wind regime and dune field development on mars and other planetary surfaces

geologic history of the polar regions of mars based on mars global surveyor data i noachian and hesperian periods during the noachian period the south polar region of mars underwent intense cratering construction of three groups of volcanoes widespread contractional deformation resurfacing of low areas and local dissection of valley networks no evidence for polar deposits ice sheets or glaciation is recognized south polar hesperian geology is broadly characterized by waning impacts volcanism and tectonism emplacement of the polar dorsa argentea formation daf occurred during the hesperian period mars orbiter laser altimeter topographic data and mars orbiter camera images elucidate stratigraphic morphologic and topographic relations permitting the dividing of the daf into eight members which surround and underlie about half of the amazonian south polar layered deposits the lobate fronts and lack of typical volcanic flow morphology of the six plains units indicate that they may be made up of debris flows we think that these flows tens of meters to 200 m thick may have originated by the discharge of huge volumes of slurry fluidized by ground water or liquid co2 perhaps triggered by local impacts igneous activity or basal melting beneath polar deposits the cavi and rugged members include irregular depressions that penetrate the subsurface some of the pits have raised rims the depressions may have formed by collapse due to expulsion of subsurface material in which local explosive activity built up the raised rims further smaller eruptions of volatile rich material may have resulted in narrow sinuous channel deposits within aggrading fine grained unconsolidated material perhaps produced by gaseous discharge of subsurface volatiles preferential erosion of the latter material could have produced the dorsa argentea type sinuous ridges associated mainly with the daf alternatively the ridges may be eskers but the lack of associated glacial and fluvial morphologies casts doubt on this interpretation the knobby degraded materials forming scandia colles may represent the only noachian geologic record exposed in the north polar region most of the north polar region was buried by water or debris ocean sediments during the hesperian period originating from uplands areas and perhaps knobby terrains in the northern plains the sediments either mantle or were deformed by wrinkle ridges radial and concentric to utopia basin and concentric to northern tharsis sources of stress probably included sediment loading in the northern plains and regional magmatic and loading activity at tharsis polar layered deposits began piling up during the early amazonian or later

wind driven particle mobility on mars insights from mars exploration rover observations at el dorado and surroundings at gusev crater 1 the ripple field known as el dorado was a unique stop on spirit s traverse where dust raising active mafic sand ripples and larger inactive coarse grained ripples interact illuminating several long standing issues of martian dust mobility sand mobility and the origin of transverse aeolian ridges strong regional wind events endured by spirit caused perceptible migration of ripple crests in deposits sse of el dorado erasure of tracks in sandy areas and changes to dust mantling the site localized thermal vortices swept across el dorado leaving paths of reduced dust but without perceptibly damaging nearly cohesionless sandy ripple crests from orbit winds responsible for frequently raising clay sized dust into the atmosphere do not seem to significantly affect dunes composed of more easily entrained sand sized particles a long standing paradox this disparity between dust mobilization and sand mobilization on mars is due largely to two factors 1 dust occurs on the surface as fragile low density sand sized aggregates that are easily entrained and disrupted compared with clay sized air fall particles and 2 induration of regolith is pervasive light toned bed forms investigated at gusev are coarse grained ripples an interpretation we propose for many of the smallest linear light toned bed forms of uncertain origin seen in high resolution orbital images across mars on earth wind can organize bimodal or poorly sorted loose sediment into coarse grained ripples coarse grained ripples could be relatively common on mars because development of durable well sorted sediments analogous to terrestrial aeolian quartz sand deposits is restricted by the lack of free quartz and limited hydraulic sediment processing

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

the mars global digital dune database mgd3 global patterns of mineral composition and bedform stability abstract we present an expansion to the mars global digital dune database mgd3 describing 1 bulk dune field composition determined by fitting a mineral spectral library to thermal emission spectra tes data and 2 a morphologic stability index that measures the degree of non aeolian modification that has eroded and stabilized each dune field this paper describes results for these two components providing insight into global patterns of dune sand sources postdepositional alteration and mineral maturity consistent with the work of others the main mineral components of each analyzed dune field are feldspar pyroxene and high silica phases with minor amounts of olivine and possibly sulfate minerals subtle global scale spatial variations in olivine and feldspar abundances correspond with previously observed trends in surface mineralogy suggesting that dune sand is reflective of its regional setting and thus that aeolian sand has typically not traveled far

qaidam basin as an analog for linear dune formation in chasma boreale mars a comparative analysis abstract this paper identifies a terrestrial analog for linear dune fields in the chasma boreale located in the north polar region of mars and analyzes it to explain linear dune formation the straight indurated linear dunes are elongated downwind of dome dunes and barchans under a unimodal wind regime providing a novel research opportunity for geomorphologists to investigate the coexistence of transverse and longitudinal dunes and the effect of sediment induration on dune morphology the linear dunes around the chaerhan salt lake in the qaidam basin are good analogs for the chasma boreale linear dunes because of the similarities in dune morphology and evolution process further the effects of the indurating agents salt and ice on the formation of the linear dunes are similar in both locations in this paper we have contrasted and analyzed their dune patterns the influence of cohesive sediment and wind regimes in the two areas the formation process and underlying mechanisms that create the linear dunes are analyzed through geomorphological evidence and dune flow simulation experiments the results show that there is a remarkable morphological resemblance between the two areas cohesive sediments especially the interbedded frozen laminae on mars increase dune stability and thus allow the formation of linear dunes under a small divergence angle in a bidirectional wind regime the proto linear dune facilitates the deposition of sediment along the major axis of the dune and the lateral wind maintains and promotes the development of linear dunes we also discuss how cohesive sediment influences dune morphology and leads to a transition from barchans to linear dunes and we examine the feedback between dune form and airflow the different effects of sediment induration on dune morphology make the determination of aeolian patterns less certain which has implications for the development of climate models of mars and titan

bedform alignment in directionally varying flows many kinds of sediment bedforms are presumed to trend either normal or parallel to the direction of sediment transport for this reason the trend of bedforms observed by remote sensing or by field observations is commonly used as an indicator of the direction of sediment transport such presumptions regarding bedform trend were tested experimentally in bidirectional flows by rotating a sand covered board in steady winds transverse oblique and longitudinal bedforms were created by changing only two parameters the angle between the two winds and the proportions of sand transported in the two directions regardless of whether the experimental bedforms were transverse oblique or longitudinal as defined by the bedform trend relative to the resultant transport direction they all had trends that yielded the maximum gross transport across the bedforms the fact that many of the experimental bedforms were neither transverse nor parallel to the resultant transport direction suggests that transport directions cannot be accurately determined by presuming such alignment

wind driven erosion and exposure potential at mars 2020 rover candidate landing sites aeolian processes have likely been the predominant geomorphic agent for most of mars history and have the potential to produce relatively young exposure ages for geologic units thus identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions such as the mars 2020 rover mission that aims to explore astrobiologically relevant ancient environments here we investigate wind driven activity at eight mars 2020 candidate landing sites to constrain erosion potential at these locations to demonstrate our methods we found that contemporary dune derived abrasion rates were in agreement with rover derived exhumation rates at gale crater and could be employed elsewhere the holden crater candidate site was interpreted to have low contemporary erosion rates based on the presence of a thick sand coverage of static ripples active ripples at the eberswalde and southwest melas sites may account for local erosion and the dearth of small craters moderate flux regional dunes near mawrth vallis were deemed unrepresentative of the candidate site which is interpreted to currently be experiencing low levels of erosion the nili fossae site displayed the most unambiguous evidence for local sand transport and erosion likely yielding relatively young exposure ages the downselected jezero crater and northeast syrtis sites had high flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses both sites had relatively high estimated abrasion rates which would yield young exposure ages the downselected columbia hills site lacked evidence for sand movement and contemporary local erosion rates are estimated to be relatively low

present day formation and seasonal evolution of linear dune gullies on mars linear dune gullies are a sub type of martian gullies as their name suggests they only occur on sandy substrates and comprise very long compared to their width straight or sinuous channels with relatively small source areas and almost non existent visible deposits linear dune gullies have never been observed on terrestrial dunes and their formation process on mars is unclear here we present the results of the first systematic survey of these features in mars southern hemisphere and an in depth study of six dunefields where repeat imaging allows us to monitor the changes in these gullies over time this study was undertaken with hirise images at 25 30 cm pix and 1 m pix elevation data derived from hirise stereo images we find the latitudinal distribution and orientation of linear dune gullies broadly consistent with the general population of martian gullies they occur predominantly between 36 3 s and 54 3 s and occasionally between 64 6 s and 70 4 s they are generally oriented toward ssw at bearings between 150 and 260 we find that these gullies are extremely active over the most recent 5 martian years of images activity comprises 1 appearance of new channels 2 lengthening of existing channels 3 complete or partial reactivation and 4 disappearance of gullies we find that gully channels lengthen by 100 m per year the intense activity and the progressive disappearance of linear dune gullies argues against the hypothesis that these are remnant morphologies left over from previous periods of high obliquity millions of years ago the activity of linear dune gullies reoccurs every year between the end of winter and the beginning of spring ls 167 4 216 6 and coincides with the final stages of the sublimation of annual co ice deposit this activity often coincides spatially and temporally with the appearance of recurrent diffusing flows rdfs digitate shaped dark patches with low relative albedo up to 48 lower than the adjacent dune that encompass the active site south and ssw facing dune slopes are those which preferentially host co2 frost deposits however it is only those with angles of 20 just below the crest which possess linear dune gullies suggesting a slope limited formation process these observations provide a wealth of temporal and morphometric data that can be used to undertake numerical modeling to direct future image monitoring and guide laboratory experiments that can be used to better constrain the formation process of these features

present day development of gully channel sinuosity by carbon dioxide gas supported flows on mars martian gullies have been widely studied but their formation mechanism is still under debate their channels generally trend straight downslope but some display sinuosity seasonally active gullies are common on sand dunes and their channels have been reported to develop sinuosity here we perform a detailed analysis of a gully on a dune within matara crater 49 5 s 34 9 e where development of channel sinuosity has taken place over 5 martian years my29 33 of observation this study was performed using hirise images hirise elevation data spectroscopic crism data and a 1d gcm for surface temperature modelling the morphological evolution of the gully suggests a significant seasonal contribution of fluid each year we observed material collapse and accumulation in the alcove followed by transport events during which lateral migration and extension of the channel occur together with growth of the debris apron over one martian year the debris apron propagated by almost 140 m from an initial length of 800 m these transport events occur in the middle of winter when co2 frost is still present and are contemporaneous with the beginning of the defrosting we propose that the activity and the sinuosity development in the gully could be explained by 1 a flow composed of sand and co2 gas producing morphologies similar to those in hyper concentrated flows on earth and 2 contribution of material from alternating of the alcove source location

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

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

patterns in mobility and modification of middle and high latitude southern hemisphere dunes on mars nasa mars data analysis program mdap nnx14ao96g mdap grant nnx12aj38g nnx16aj43g 123117

scarp orientation in regions of active aeolian erosion on mars abstract the morphologies of wind formed features on mars provide diagnostic information about ancient and modern surface winds aeolian erosional features include decimeter scale ventifacts and kilometer scale yardangs but intermediate scale erosional features are less well understood understanding aeolian erosion may be critical to identifying ancient martian biosignatures cosmogenic radiation destroys complex organic molecules during prolonged exposure at the martian surface but outcrops freshly re exposed by aeolian erosion provide potential sites where biosignatures could have been protected and made recently available for sampling wind driven scarp retreat has been cited as the cause for young exposure ages measured in gale crater upcoming exploration by the mars 2020 rover will focus on jezero crater another location of extensive aeolian erosion and meter scale scarps this work is motivated by the hypothesis that retreating scarps on mars may prefer orientations that reflect the direction of erosive winds we mapped scarps in jezero and gale craters and compared their orientation distributions with local wind regimes interpreted from other aeolian indicators no strong correlation between wind direction and scarp orientation was identified the near random distribution of scarp orientations suggests that in the locations studied the dominant processes controlling scarp orientation are either processes that do not prefer an orientation e g impact or thermal fracturing processes or that turbulent flow structures form at the scale of scarp topography and obscure the regional scale signals of erosion with scarp scale eddies and flow deflection

a scaling law for aeolian dunes on mars venus earth and for subaqueous ripples abstract the linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength at which the bed destabilises to form dunes should scale with the drag length l drag s f d this scaling law is tested using existing and new measurements performed in water subaqueous ripples in air aeolian dunes and fresh snow dunes in a high pressure co2 wind tunnel reproducing conditions close to venus atmosphere and in the low pressure co2 martian atmosphere martian dunes the difficulty is to determine the diameter of saltating grains on mars a first estimate comes from photographs of aeolian ripples taken by the rovers opportunity and spirit showing grains whose diameters are smaller than on earth dunes in addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds it confirms that the small grains visualised by the rovers should be grains experiencing saltation finally we show that within error bars the scaling of with ldrag holds over almost five decades we conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on mars

aeolian processes in proctor crater on mars sedimentary history as analyzed from multiple data sets 1 proctor crater is a 150 km diameter crater in noachis terra within the southern highlands of mars the analysis leading to the sedimentary history incorporates several data sets including imagery elevation composition and thermal inertia mostly from the mars global surveyor mission the resulting stratigraphy reveals that the sedimentary history of proctor crater has involved a complex interaction of accumulating and eroding sedimentation aeolian features spanning much of the history of the crater interior dominate its surface including large erosional pits stratified beds of aeolian sediment sand dunes erosional and depositional streaks dust devil tracks and small bright bed forms that are probably granule ripples long ago up to 450 m of layered sediment filled the crater basin now exposed in eroded pits on the crater floor these sediments are probably part of an ancient deposit of aeolian volcaniclastic material since then some quantity of this material has been eroded from the top layers of the strata small bright dune forms lie stratigraphically beneath the large dark dune field relative to the large dark dunes the bright bed forms are immobile although in places their orientations are clearly influenced by the presence of the larger dunes their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill dust devil tracks form during the spring and summer following a west southwesterly wind early in the spring the dust devils are largely restricted to dark patches of sand as the summer approaches dust devil tracks become more plentiful and spread to the rest of the crater floor indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils the dark dunes contain few dust devil tracks suggesting that accumulated dust is swept away directly by saltation rather than by the passage of dust devils spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt like materials the average thermal inertia calculated from thermal emission spectrometer bolometric temperatures is 277 17 j m 2 s 0 5 k 1 leading to an effective grain size of 740 170 mm which is consistent with coarse sand and within the range expected for martian sand the coarse sand that composes the large dune field may have originated from outside the crater saltating in from the southwest most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried the sand was transported to the east center of the crater floor where beneath the present day dunes a 50 m high mound of sand has accumulated dune slip faces indicate a wind regime consisting of three opposing winds some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms the combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime which produces the large reversing transverse and star dunes that dominate the dune field the dark dunes have both active slip faces and seemingly inactive slip faces suggesting that the dunes vary spatially in their relative activity nevertheless the aeolian activity that has dominated the history of proctor crater still continues today index terms 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5410 planetology solid surface planets

mars observer camera the mars observer camera moc is a three component system one narrow angle and two wide angle cameras designed to take high spatial resolution pictures of the surface of mars and to obtain lower spatial resolution synoptic coverage of the planet s surface and atmosphere the cameras are based on the push broom technique that is they do not take frames but rather build pictures one line at a time as the spacecraft moves around the planet in its orbit moc is primarily a telescope for taking extremely high resolution pictures of selected locations on mars using the narrow angle camera areas ranging from 2 8 km 2 8 km to 2 8 km 25 2 km depending on available internal digital buffer memory can be photographed at about 1 4 m pixel additionally lower resolution pictures to a lowest resolution of about 11 m pixel can be acquired by pixel averaging these images can be much longer ranging up to 2 8 500 km at 11 m pixel high resolution data will be used to study sediments and sedimentary processes polar processes and deposits volcanism and other geologic geomorphic processes the moc wide angle cameras are capable of viewing mars from horizon to horizon and are designed for low resolution global and intermediate resolution regional studies low resolution observations can be made every orbit so that in a single 24 hour period a complete global picture of the planet can be assembled at a resolution of at least 7 5 km pixel regional areas covering hundreds of kilometers on a side may be photographed at a resolution of better than 250 m pixel at the nadir such images will be particularly useful in studying time variable features such as lee clouds the polar cap edge and wind streaks as well as acquiring stereoscopic coverage of areas of geological interest the limb can be imaged at a vertical and along track resolution of better than 1 5 km different color filters within the two wide angle cameras permit color images of the surface and atmosphere to be made to distinguish between clouds and the ground and between clouds of different composition

mars global digital dune database mgd3 north polar region mc 1 distribution applications and volume estimates the mars global digital dune database mgd3 now extends from 90 n to 65 s the recently released north polar portion mc 1 of mgd3 adds 844 000 km2 of moderate to large size dark dunes to the previously released equatorial portion mc 2 to mc 29 of the database the database available in gis and tabular format in usgs open file reports makes it possible to examine global dune distribution patterns and to compare dunes with other global data sets e g atmospheric models mgd3 can also be used by researchers to identify areas suitable for more focused studies the utility of mgd3 is demonstrated through three example applications first the uneven geographic distribution of the dunes is discussed and described second dune derived wind direction and its role as ground truth for atmospheric models is reviewed comparisons between dune derived winds and global and mesoscale atmospheric models suggest that local topography may have an important influence on dune forming winds third the methods used here to estimate north polar dune volume are presented and these methods and estimates 1130 km3 to 3250 km3 are compared with those of previous researchers 1158 km3 to 15 000 km3 in the near future mgd3 will be extended to include the south polar region published in 2011 this article is a us government work and is in the public domain in the usa