martian crater dark streak lengths explanation from wind tunnel experiments the mechanism determining the length of dark erosional type id streaks near craters and hills on the surface of mars is investigated using mariner 9 images and the results of wind tunnel studies greeley et al 1974 iversen et al 1975 and 1976 an empirical model of time dependent growth of crater wake streaks in the downwind direction involving deflation by sand grain saltation is developed and shown to give relatively good agreement with streak growth rates observed over a 38 day period of mariner observations and with the streak length crater diameter and streak length crater height ratios analyzed statistically by lee 1984 this time dependent mechanism is thus considered a reasonable alternative for dark streaks to the blocking model proposed by lee for both bright and dark streaks preliminary analysis of further wind tunnel experiments iversen et al 1982 supports the blocking model of bright streak formation

the martian surface the past four years have been particularly fruitful for martian research as the enormous volumes of data collected during the viking mission became readily available to the general science community and as reformatting of the remote sensing data into cartographic products made the data more useable the 1 5 000 000 scale map series is complete and 1 2 000 000 scale controlled mosaics of the entire planet are nearing completion in addition 1 500 000 scale mosaics have been prepared of about thirty local areas a uniform scale digital imaging data base is in preparation batson 1986 and the infrared data have been reformatted to make it more accessible to the general user martin and kieffer 1985

numerical simulations of waves over large crater topography in the atmosphere abstractnumerical simulations are used to investigate waves generated by flow over crater topography of diameter 100 km in an idealized atmosphere the atmosphere is stratified with a constant buoyancy frequency profile and the background wind is constant this study describes the development of a low level jet along the upstream crater slope and its interaction with the cooler air within the crater valley this interaction results in a hydraulic jump like structure that acts as a modified topography forcing a beam of secondary waves the hydraulic jump is formed by a retreating gravity current as the cool air within the crater readjusts after the initial tilting of potential temperature contours a two dimensional simulation is used to compare features such as wave overturning in two and three dimensions several variations on the atmosphere s profile are considered including an atmosphere with reduced constant stratification and an atmosphere that is unstratified within the crater these results indic

radar altimetry of large martian craters abstract mars topography in the 23 to 22 latitude band has been measured by the goldstone 13 cm radar during the 1971 1982 oppositions a total of 108 scans were produced each scan spans several tens of degrees in longitude the longest scan spans 133 8000 the vertical resolution generally is better than 200 m with some exceptions the areal resolution is 0 16 8 km in longitude and 1 30 80 km in latitude on regional scales elevation differences of as much as 3 km over less than 10 longitude have been observed aeolis memnonia most local relief is provided by structural elements of impact craters one hundred fifty two complex degraded craters some as small as 25 km in diameter have been identified in this data set repeated scans of the same craters yield nearly identical elevation profiles measured crater depths rarely exceed 2 5 km depths of the most degraded craters in the sample are a weak function of crater diameter depths of the largest craters d 125km show no functional relationship to diameters measured rim heights rarely exceed several hundred meters structures with no discernible rim e g ladon have retained a basin shape low exterior relief rather than overall low relief seems to be the distinguishing characteristic of large degraded craters included in the goldstone sample craters or basins that serve as sinks for major channel systems e g gusev ladon appear to be as deep as comparable structures not associated with such systems suggesting that processes other than fluvial sedimentation contributed to crater shallowing

recent flood lavas in the elysium region of mars abstract a vast area of smooth plains in southeastern elysium here referred to as the cerberus formation is interpreted to be of volcanic origin surface morphology lobate edges of the unit the identification of vents low shields and the embayment relation of the unit with adjacent older units all suggest a volcanic origin the plains were formed by the eruption of low viscosity lavas that filled a topographic depression in southeast elysium and then flowed into western amazonis planitia flow into western amazonis was facilitated by a series of channels carved by an earlier fluvial episode which were exploited by lavas as they moved down slope crater frequencies and stratigraphic relations indicate that the unit is very young upper amazonian the presence of such young flood lavas indicates 1 late in martian history large scale eruptions of low viscosity lava was still possible b sufficient heat remained in the mantle to mobilize large quantities of magma and c flood volcanism either continued or resumed in elysium after activity of the large central volcanoes had ceased each of these points are important considerations in understanding the martian thermal and volcanic history

the sedimentology and dynamics of crater affiliated wind streaks in western arabia terra mars and patagonia argentina abstract wind streaks comprise recent aeolian deposits that have been extensively documented on venus earth and mars martian wind streaks are among the most abundant surface features on the planet and commonly extend from the downwind margins of impact craters previous studies of wind streaks emerging from crater interior deposits suggested that the mode of emplacement was primarily related to the deposition of silt sized particles as these settled from plumes we have performed geologic investigations of two wind streaks clusters one situated in western arabia terra a region in the northern hemisphere of mars and another in an analogous terrestrial site located in southern patagonia argentina where occurrences of wind streaks emanate from playas within maar craters in both these regions we have identified bedforms in sedimentary deposits on crater floors along wind facing interior crater margins and along wind streaks these observations indicate that these deposits contain sand sized particles and that sediment migration has occurred via saltation from crater interior deposits to wind streaks in arabia terra and in patagonia wind streaks initiate from crater floors that contain lithic and evaporitic sedimentary deposits suggesting that the composition of wind streak source materials has played an important role in development spatial and topographic analyses suggest that regional clustering of wind streaks in the studied regions directly correlates to the areal density of craters with interior deposits the degree of proximity of these deposits and the craters rim to floor depths in addition some but not all wind streaks within the studied clusters have propagated at comparable yearly earth years rates extensive saltation is inferred to have been involved in its propagation based on the studied terrestrial wind streak that shows ripples and dunes on its surface and the martian counterpart changes orientation toward the downslope direction where it extends into an impact crater

classification of wind streaks on mars abstract a classification of martian wind streaks has been developed to assist in investigations of eolian transport and related meteorological phenomena on mars streaks can be grouped by their albedo contrast with their surroundings and by the presence of either topographic obstacles or sediment deposits at their points of origin the vast majority of wind streaks can be included in three categories 1 bright streaks with no source deposit interpreted to be formed by preferential deposition of dust from suspension 2 dark streaks with no source deposit interpreted to be formed by preferential erosion of bright dust and its removal in suspension 3 dark streaks associated with deposits of sediment interpreted to be formed by deposition of dark material moved by saltation the orientations of the different streak types are distinctive and reflect both global flow patterns and slope controlled winds the wind directions derived from streaks and the geographical distribution of the features show a strong north south asymmetry consistent with the fact that perihelion and hence maximum wind activity occurs near southern summer solstice

landscape evolution and human occupation during the archaic period on the northern plains recent archaeological excavations at a deeply stratified site in northwest calgary alberta have uncovered four occupation layers spanning the interval from 8000 to 2000 bp depending on the dating one accepts for the holocene thermal maximum two or more of these occupations occurred during this interval of aridity this site thus provides a record of human occupation during the archaic middle prehistoric i period in the calgary area more importantly the site occurs in an upland setting apparently far removed from reliable sources of water and normal environments of deposition yet the cultural deposits occur in sediments which extend 2 m below surface and include five sedimentary units as well as a minimum of three pedogenic units this paper presents the results of geoarchaeological research on the changing landscape for the site and notes the implications of these changes for the study of archaic manifestations on the northern plains

wind streaks on mars meteorological control of occurence and mode of formation abstract why do some craters on mars produce depositional wind streaks while others produce erosional ones there is no evidence to suggest that crater morphology or topography plays the determining role some craters can form either type of streak at different times of the martian year suggesting that the controlling factor is meteorological we propose that atmospheric stability is the determining factor a stable atmosphere should lead to blocking of the wind flow by crater rims producing wind shadows over distances comparable to those of observed bright streaks such conditions should prevail in a belt about the equator at the time of major dust storms as the atmosphere becomes more transparent following the end of the dust storms the rate of surface heating increases and the stability of the atmosphere is reduced under such conditions blocking is not expected flow over obstacles results in increased surface stress downwind conditions which encourage the formation of erosional dark streaks these ideas are shown to be consistent with the seasons at which erosional and depositional streaks are formed as well as with their distribution on the planet specifically the scheme explains why craters which have both erosional and depositional streaks occur only within a very restricted latitude belt

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

dust streaks on mars global mapping and photometry of selected areas on mars are used to investigate the nature of bright and dark wind streaks that extend from topographic obstacles occurrence of both bright and dark streaks is strongly latitude dependent and is only weakly correlated with surface properties such as albedo and thermal inertia data on the colors albedos and phase behavior of streaks are consistent with models of bright streaks as mosaics of plains material and brighter redder dust less than 20 of the ground need be covered by the optically thick dust in the brightest parts of the streaks the amount of dust in optically thick layers could be as little as 10 3 g cm2 dark streaks can be interpreted as erosional windows in a patchy dust cover our model of dust deposition in optically thick patches is sedimentologically different from scenarios involving the deposition of ubiquitous optically thin layers it has the advantage that large amounts of dust can be deposited without affecting regional albedos

aeolian features on venus preliminary magellan results magellan synthetic aperture radar data reveal numerous surface features that are attributed to aeolian or wind processes wind streaks are the most common aeolian feature they consist of radar backscatter patterns that are high low or mixed in relation to the surface on which they occur a data base of more than 3400 wind streaks shows that low backscatter linear forms long narrow streaks are the most common and that most streaks occur between 17 s to 30 s and 5 n to 53 n on smooth plains moreover most streaks are associated with deposits from certain impact craters and some tectonically deformed terrains we infer that both of these geological settings provide fine particulate material that can be entrained by the low velocity winds on venus turbulence and wind patterns generated by the topographic features with which many streaks are associated can account for differences in particle distributions and in the patterns of the wind streaks thus some high backscatter streaks are considered to be zones that are swept free of sedimentary particles to expose rough bedrock other high backscatter streaks may be lag deposits of dense materials from which low density grains have been removed dense materials such as ilmenite or pyrite have dielectric properties that would produce high backscatter patterns wind streaks generally occur on slopes 2 and tend to be oriented toward the equator consistent with the hadley model of atmospheric circulation in addition to wind streaks other aeolian features on venus include yardangs and dune fields the aglaonice dune field centered at 25 s 340 e covers 1290 km 2 and is located in an ejecta flow channel from the aglaonice impact crater the meshkenet dune field located at 67 n 90 e covers 17 120 km 2 in a valley between ishtar terra and meshkenet tessera wind streaks associated with both dune fields suggest that the dunes are of transverse forms in which the dune crests are perpendicular to the prevailing winds dunes on venus signal the presence of sand size 60 to 2 000 m grains the possible yardangs are found at 9 n 60 5 e about 300 km southeast of the crater mead although most aeolian features are concentrated in smooth plains near the equator the occurrence of wind streaks is widespread and some have been found at all latitudes and elevations they demonstrate that aeolian processes operate widely on venus the intensity of wind erosion and deposits however varies with locality and is dependent on the wind regime and supply of particles

surface properties of the pettit wind streak on mars implications for sediment transport abstract pettit crater 12 n 174 w is associated with a complex wind streak consisting of both type i bright streak and type ii dark streak materials broadband albedo measurements of the streak indicate a minimum of 20 and a maximum of 32 with 27 on the surrounding plains the darkest materials have the highest thermal inertias which can be related to an effective grain diameter typical of medium sand most of the dark streak materials have thermal inertias representative of fine sand the material most easily set in motion by the wind on mars the bright portions of the streak have thermal inertias higher than that of the surrounding plains the bright streak values are representative of very fine sand differences between temperatures measured at 11 and 20 m indicate there is no difference in the areal abundance of unresolved high thermal inertia materials e g blocks bedrock between the pettit streak and the surrounding plains the dark streak material is consistent with models involving sand saltation and transport but the bright streak thermal inertia is not consistent with a volumetrically significant enhancement of unconsolidated dust in the streak

debris accumulations of co2 ice in the south polar residual cap of mars longevity and processes abstract the residual south polar cap rspc of mars is a thin covering of co2 ice resting on water ice rich deposits as such it is a likely indicator of the net effects of recent polar climate this covering has had minor changes in outline for the period of spacecraft observation piqueux and christensen 2008a and estimates of its recent mass balance suggest fractionally small changes in its volume thomas et al 2016 pit growth by scarp retreat malin et al 2001 byrne and ingersoll 2003a thomas et al 2005 2013 is a major relatively easily measured component of the cap s mass balance this scarp retreat is only the beginning of a process fracturing slumping and sublimation byrne et al 2008 thomas et al 2009 lead to production of a trail of debris this study focuses on that debris using spacecraft imaging data the rough relatively dark debris forms ubiquitous ramps typically tens of m wide around scarps within pits or on perimeters of mesas much wider accumulations of debris debris fields mimic distinctive scalloped outlines of mesas and are observed to originate by merging of expanding pits within a mesa the subsequent evolution of debris fields includes repeated year to year local relief inversions that involve trapping and retention of seasonal ice in low areas that effectively reduce the vertical loss rates complete loss of the co2 debris from a surface of water ice rich polar layered deposits pld can initiate new net accumulation of co2 ice the longevity of some debris fields essentially instances of slow downwasting appear to facilitate relief inversion on large scales by allowing the surrounding areas to accumulate new co2 ice and to thicken relative to the debris fields

martian intracrater splotches occurrence morphology and colors abstract martian intracrater splotches and related streaks are studied with global data on their occurrence and regional data on color and morphology the fraction of craters with splotches is greatest at high latitudes splotch occurrence is not strongly correlated with surface properties such as albedo and thermal inertia except where these correlate with substantial sediment cover large numbers of splotches are or include dunes especially at high southern latitudes color data show that the dune and nondune materials in splotches are part of one related group of materials that may be of similar composition but varying particle sizes the color data also show that some streaks are simply material deflated from splotches and mixed with local plains material while other streaks are more complex and may involve erosion of thin surface layers by material blown from the splotches splotches appear to be trapped eolian sand but probably have been formed by a great variety of mechanisms a large percentage of craters with splotches show evidence of complex histories of sediment deposition and erosion many splotches may be lag deposits from erosion of regional sediment cover present sediment budgets in splotches are not known but there is some evidence for loss of material and no evidence for resupply from outside the craters

moc observations of the 2001 mars planet encircling dust storm abstract from 15 september 1997 through 21 january 2006 only a single planet encircling martian dust storm was observed by mgs moc the onset of the storm occurred on 26 june 2001 l s 184 7 earliest recorded to date it was initiated in the southern mid to low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in malea and in hellas basin l s 176 2 184 4 the initial expansion of the storm though asymmetric was very rapid in all directions 3 32 m s 1 the main direction of propagation however was to the east with the storm becoming planet encircling in the southern hemisphere on l s 192 3 several distinct centers of active dust lifting were associated with the storm with the longest persisting for 86 sols syria claritas these regional storms helped generate and sustain a dust cloud haze which reached an altitude of about 60 km and a peak opacity of dust 5 0 by l s 197 0 the cloud had encircled the entire planet between 59 0 s and 60 0 n obscuring all but the largest volcanoes the decay phase began around l s 200 4 with atmospheric dust concentrations returning to nominal seasonal low levels at l s 304 0 exponential decay time constants ranged from 30 117 sols the storm caused substantial regional albedo changes darkening and brightening as a result of the redistribution removal and deposition of a thin veneer of surface dust at least 0 1 11 1 m thick it also caused changes in meteorological phenomena i e dust storms dust devils clouds recession of the polar caps and possibly surface temperatures that persisted for just a few weeks to more than a single mars year the redistribution of dust by large annual regional storms might help explain the long period 30 years between the largest planet encircling dust storms events

late holocene land use at orstad jaeren southwestern norway evidence from pollen analysis and soil micromorphology abstract pollen analysis was combined with radiocarbon dating physical chemical and biological soil analyses and soil micromorphology to investigate the prehistoric land use at orstad in jaeren southwestern norway orstad is an early bronze age clearance cairn field in a cultural landscape with traces of land use back to the neolithic samples were mainly collected from an 84 m long excavated trench with mainly podzolic soils although pollen preservation was poor it was possible to differentiate five phases in the local vegetation and land use history human impact on the site could be traces back to about 4400 4000 bp uncal 3045 2600 cal bc wheat and barley have been cultivated at orstad during a period from ca 3600 bp uncal 1945 1750 cal bc until the older iron age when heather vegetation began to spread on the site soil micromorphology revealed different soil management practices for this time period the soils seem to have been cleared by fire prior to cultivation until ca 3200 bp uncal 1610 1455 cal bc then new cultivation fields were laid out on higher levels and seem to have been improved by adding of organic materials mainly turves taken from podzolic top soils and peats from nearby localities

mars wind streak production as related to obstacle type and size abstract the characteristics of wind streaks associated with martian craters and hills in the size range of 100 m to 80 km corresponding to obstacle heights of a few to several hundred meters have been analyzed from viking orbiter images both dark erosional and bright depositional streaks form over the entire obstacle size range but there are preferred obstacle sizes for producing streaks bright streaks form more readily in association with relatively smaller obstacles than do dark streaks small obstacles produce both types of streaks more effectively than do large ones hills produce streaks as effectively as do craters of comparable height alternative explanations of bright streak formation are evaluated in terms of their ability to account for these observations the most satisfactory models invoke blocking of atmospheric flow downwind of an obstacle and consequent deposition of dust within the sheltered zone

impact generated winds on mars abstract bright and dark wind streaks across mars record wind patterns related to atmospheric circulation in some cases these streaks represent erosion of a surface veneer in others they indicate sand grains mobilized by strong vortices shed off of positive relief such as crater rims while many streaks change length or orientation over time others not only remain unchanged but also may indicate a completely different wind direction these permanent streaks could reflect past circulation patterns in response to conditions related to orbital forcing e g thomas and veverka 1979 veverka et al 1981 here however we focus on a subset of permanent wind streaks unrelated to global circulation rather to impact generated winds that can extend more than 500 km away from the crater nighttime images from the mars odyssey s thermal emission imaging system themis reveal certain large craters 15 km in diameter having sets of thermally bright streaks that radiate from certain fresh impact craters these streaks extend from pre existing topographic highs crater rims wrinkle ridges beyond the continuous ejecta deposits to more than 6 crater radii unrelated to secondary craters for illustration this contribution primarily focuses on the 20 km diameter santa fe crater in chryse planitia context camera ctx images reveal that these streaks correspond to zones of erosion the thermally bright rays in nighttime images correlate with regions where coarser materials have been exposed not always resolved even in hirise images models of the impact process indicate impact generated vapor most likely generated intense winds that scoured the region well before arrival of secondary craters and later ejecta run out flows pre existing relief such as crater rims disturbed this flow and generated intense cross flow instabilities resulting in long parallel streaks

visual and infrared observations of wind streaks on mars abstract estimation of surface properties and physical setting of three common martian wind streak types bright dark and splotch related provides constraints on models of the formation and variability of streaks bright streaks form independently of surface properties other than local topography this is consistent with their formation being due to deposition of atmospheric dust in the lee of topographic features although they are widespread on mars dark streaks are noted as variable only in regions near 30 s latitude and elevations between 3 and 7 km and are associated with dark surfaces that have relatively high thermal inertias splotch related streaks occur at elevations between 0 and 6 km and in regions of relatively high thermal inertia splotch related streaks occur near the boundaries of thermally defined regions such as the south polar cap and other areas of either low or high thermal inertia these thermal conditions are responsible for the production of surface winds which form and modify these streaks the source of sidements which form splotch related streaks varies from dunes to well indurated stratified deposits regional studies of the various types in syrtis major syria planum claritas fossae oxia palus mesogea and pettit craters and noachis confirm that the correlations found at the global level occur at regional scales

structure and dynamics of the upper mantle beneath the alpine himalayan orogenic belt from teleseismic tomography abstract the upper mantle structure beneath the alpine himalayan orogenic belt ahb at depths from 100 to 500 km has been studied by its tomographic inversion of p wave travel times from earthquakes that occurred in the region and were recorded by the worldwide seismological network at teleseismic distances from the isc catalogues the resulting maps were obtained as a sum of independent inversions in about 60 overlapping blocks 600 800 km in diameter this approach is similar to high frequency spatial filtration and allows investigation of much subtler structures than in global inversion high velocity linear patterns along the ahb have been interpreted as traces of continental or oceanic lithosphere sinking to the upper mantle under the effect of active regional compression the tomographic maps show well pronounced traces of subduction in the region of cretan arc hindukush and burma also confirmed by independent data as well as other less certain evidence of subduction positive anomalies in the western part of the ahb are attributed to subduction in the area of cyprus and along the caucasus kopet dagh lut plate in the tomographic maps one can see traces of the subducted indian slab under western part of himalayas beneath eastern himalayas the upper mantle is rather hot zones of sinking lithosphere are traceable around the tarim block a strong low velocity anomaly in mongolia is apparently related to the hangai plume whose existence was inferred from geological and geophysical evidence

temporal changes in the cerberus region of mars mariner 9 and viking comparisons abstract as in seen from comparisons of mariner 9 images obtained in 1972 and viking orbiter 1 images obtained in 1978 several changes have occurred in the cerberus region of mars changes in the boundary of the low albedo feature resulted in an increase of the total area of cerberus by slightly more than 1 although the southwestern boundary had shifted as much as 90 km relative darkening of cerberus has resulted in a more uniform tone and is accompanied by the disappearance of dark filamentary markings although several bright streaks within cerberus changed in length neither lengthening nor shortening of the streaks predominated however changes in streak direction indicate a clockwise rotation of mean streak azimuth between 1972 and 1978 these changes in the outline and appearance of cerberus can best be explained by eolian redistribution and removal of bright material during major dust storms volcanic flow fronts which show through the albedo feature indicate that the contrast between cerberusand the surrounding light plains is not due to a difference in lithology but to the distribution of surficial deposits because of local topographic influences on the regional atmospheric circulation patterns it is probable that cerberus will retain a similar appearance and location

the role of geoarchaeology in extending our perspective specialists and the general public alike are very aware of human impacts on our environment climate change deforestation desertification soil erosion and other topics are currently much in the news but human influence on the environment is not a new phenomenon geoarchaeologists study the traces of human interactions with the geosphere dating back to ancient times as well as up to and in the present geoarchaeological investigations provide the key to recognizing landscape and environmental change within a region as well as reconstructing ancient landscapes and palaeoclimatic regimes such an interdisciplinary approach makes it possible to interpret the ways that humans affect the geosphere through such things as subsistence and resource exploitation activities settlement location and local and regional land use patterns this approach also allows us to determine the effects of environmental change on human societies for millennia humans have been coping with or provoking environmental change we have exploited extracted over used but also in many cases nurtured the resources that the geosphere offers in the geoarchaeological perspective human life has never been separate from nature geoarchaeology can thus provide a more inclusive and longer term view of human geosphere interactions and serve as a valuable aid to those who try to determine sustainable policies for