dark slope streaks on mars are aqueous processes involved 1 concentrations of dark slope streaks occur in the equatorial latitudes of mars mostly where magmatic driven activity dominates the geologic record although originally ascribed to wet debris flows all the most recent published hypotheses concerning these features focus on processes which disturb a brighter dusty mantle to expose a darker substrate these mechanisms invoke dry mass wasting or eolian processes excluding a role for water in light of the geographic geologic and morphologic considerations and the new information provided from the mars orbital camera and the mars orbital data altimeter we reexamine fluvial processes as a viable explanation for some of the dark slope streaks in our opinion two contrasting processes for the formation of dark slope streaks dust avalanching and spring discharge represent endpoints on a continuum of progenitors it may be that some of these features result from dry mass wasting or eolian processes some from fluvial processes and some from a mechanism s not yet conceived a spring discharge origin for the formation of the dark slope streaks has profound implications including mars having limited but currently active fluvial processes acting upon its surface as well as near surface aquifers

first in situ analysis of dust devil tracks on earth and their comparison with tracks on mars in this study we report about the first in situ analysis of terrestrial dust devil tracks ddts observed in the turpan depression desert in northwestern china passages of active dust devils remove a thin layer of fine grained material 63 m cleaning the upper surface of coarse sands 0 5 1 mm this erosional process changes the photometric properties of the upper surface causing the albedo differences within the track to the surroundings measurements imply that a removal of an equivalent layer thickness of 2 m is sufficient to form the dark dust devil tracks our terrestrial results are in agreement with the mechanism proposed by greeley et al 2005 for the formation of ddts on mars

hirise observations of slope streaks on mars 1 images from the high resolution imaging science experiment have revealed new details on the morphologic and topographic characteristics of slope streaks on mars over 1500 hirise images were analyzed with 78 unique image sites having slope streaks images with low sun illumination reveal that dark slope streaks have topographic relief where streaked surfaces are lower than their surroundings slope streaks often initiate below localized features such as rock outcrops individual boulders and impact craters they are also abundant in great numbers within the blast zones of small young impact craters 10 50 m in diameter these observations suggest that slope streaks can be triggered by localized disturbances such as rockfalls and impact blasts seismic activity from external e g impacts or internal forces could also trigger slope streaks the topographic relief and triggering mechanisms of slope streaks seem to best fit models that involve dry dust avalanches martian slope streaks and meters thick avalanche scars are part of a continuum of active mass wasting features at meter to sub meter scales

three decades of slope streak activity on mars slope streaks are surficial mass movements that are abundant in the dust covered regions of mars targeting of slope streaks seen in viking images with the mars orbiter camera provides observations of slope streak dust activity over two to three decades in all study areas new and persisting dark slope streaks are observed slope streaks disappeared in one area with persisting streaks nearby new slope streaks are found to be systematically darker than persisting streaks which indicates gradual fading far more slope streaks formed at the study sites than have faded from visibility the rate of formation at the study sites was 0 03 new slope streaks per existing streak per mars year bright slope streaks do not presently form in sudden events as dark slope streaks do instead bright streaks might form from old dark slope streaks perhaps transitioning through a partially faded stage

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

recent rheologic processes on dark polar dunes of mars driven by interfacial water abstract in springtime on hirise images of the southern polar terrain of mars flow like or rheologic features were observed their dark color is interpreted as partly defrosted surface where the temperature is too high for co2 but low enough for h2o ice to be present there these branching streaks grow in size and can move by an average velocity of up to about 1 m day and could terminate in pond like accumulation features the phenomenon may be the result of interfacial water driven rheologic processes liquid interfacial water can in the presence of water ice exist well below the melting point of bulk water by melting in course of interfacial attractive pressure by intermolecular forces van der waals forces e g curvature of water film surfaces and e g by macroscopic weight acting upon ice this melting phenomenon can be described in terms of premelting of ice it is a challenging consequence that liquid interfacial water unavoidably must in form of nanometric layers be present in water ice containing soil in the subsurface of mars it is the aim of this paper to study possible rheologic consequences in relation to observations which seem to happen at sites of dark polar dunes on mars at present the model in this work assumes that interfacial water accumulates at the bottom of a translucent water ice layer above a dark and insolated ground this is warmed up towards the melting point of water the evolving layer of liquid interfacial water between the covering ice sheet and the heated ground is assumed to drive downward directed flow like features on slopes and it can at least partially infiltrate seep into a porous ground there in at least temporarily cooler subsurface layers the infiltrated liquid water refreezes and forms ice the related stress built up is shown to be sufficient to cause destructive erosive processes the above mentioned processes may cause change in the structure and thickness of the covering ice and or may cause the movement of dune grains all these processes may explain the observed springtime growing and downward extension of the slope streaks analyzed here

modelling of strata movement with a special reference to caving mechanism in thick seam coal mining abstract caving of top coal behind the face is the key factor affecting the efficiency of production at thick coal seams during production of top coal by caving behind the face not only is a significant amount of coal lost in the goaf but also the coal drawn by means of caving is usually diluted considerably with surrounding rock therefore it is not possible to carry out an efficient production operation unless caving of top coal behind the face is optimized in this paper results of 3 d modelling of the top coal caving mechanism at the m3 longwall panel of omerler underground mine located at tuncbilek turkey are presented by using a finite difference code called flac 3d according to modelling results a 1 5 2 0 m thick layer of coal just above the shield supports is well fractured however 3 0 3 5 m thick layer of coal above the well fractured part is either not fractured or fractured in the form of large blocks leading to obstruction of windows of shields during coal drawing it is concluded that in order to decrease dilution and increase extraction ratio and production efficiency the top coal should be as uniformly fractured as much as possible hence an efficient and continuous coal flowing behind the face can be maintained a special pre fracture blasting strategy just sufficient enough to form cracks in the top coal is suggested by means of comparing results from numerical modelling

stratigraphy structure and volcanic evolution of the pico teide pico viejo formation tenerife canary islands abstract the structure and volcanic stratigraphy of the pico teide pico viejo pt pv formation deriving from the basanite phonolite stratovolcanoes pt and pv and numerous flank vent systems are documented in detail based on new field and photogeologic mapping geomorphologic analysis borehole data and petrological and geochemical findings results provide insight into the structure and evolution of the pt pv magma system and the long term cyclic evolution of tenerife s post shield volcanic complex the pt pv formation comprises products of central volcanism mainly emplaced into the las canadas caldera lcc and contemporaneous products from adjacent rifts pt pv central volcanic products become more differentiated up section with felsic lavas dominating the recent output of the system this is attributed to the evolution of a shallow magma reservoir beneath pt that was emplaced early in the pt pv cycle on the intra caldera segment of tenerife s post shield rift system the rift axis has been the focus of pt pv intrusive and eruptive activity and has controlled the location of the stratocones the current geometry of the rifts reflects a major structural reorganisation defining the start of the pt pv cycle at 0 18 ma namely the truncation of the north side of the lcc lce by the giant icod landslide the internal stratigraphy of the pt pv formation suggests that pt developed early with pv developing as a satellite vent activity has since alternated between pt and pv due to episodes of vent blockage or chamber sealing these processes have allowed significant volumes of phonolitic magmas to develop and accumulate within the pt chamber which have vented through radial dike systems during tumescence episodes and from the rift system which has permitted lateral magma transport the pt pv magma system is a potentially hazardous source of future felsic eruptive activity on tenerife

geologic map of the northern hemisphere of vesta based on dawn framing camera fc images abstract the dawn framing camera fc has imaged the northern hemisphere of the asteroid 4 vesta at high spatial resolution and coverage this study represents the first investigation of the overall geology of the northern hemisphere 22 90 n quadrangles av 1 2 3 4 and 5 using these unique dawn mission observations we have compiled a morphologic map and performed crater size frequency distribution csfd measurements to date the geologic units the hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to 200 km in diameter the most widespread unit is a plateau cratered highland unit similar to although of lower elevation than the equatorial vestalia terra plateau large scale troughs and ridges have regionally affected the surface between 180 e and 270 e these tectonic features are well developed and related to the south pole veneneia impact saturnalia fossae trough unit elsewhere on the hemisphere they are rare and subdued saturnalia fossae cratered unit in these pre rheasilvia units we observed an unexpectedly high frequency of impact craters up to 10 km in diameter whose formation could in part be related to the rheasilvia basin forming event the rheasilvia impact has potentially affected the northern hemisphere also with s n small scale lineations but without covering it with an ejecta blanket post rheasilvia impact craters are small

the role of the wind transported dust in slope streaks activity evidence from the hrsc data abstract slope streaks are gravity driven albedo features observed on martian slopes since the viking missions the debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting a systematic mapping of slope streaks from the high resolution stereo camera is presented in this paper two regions known for their slope streaks activity have been studied the first one is located close to cerberus lava flow and the second one is inside the olympus mons aureole the statistics of slope streaks shapes measured from orthorectified images confirm previous results from mars orbiter camera surveys preferential orientations of slope streaks are reported slope streaks occur preferentially on west facing slopes at latitudes lower than 30 n for olympus and on south west facing slopes for cerberus wind directions derived from a general circulation model during the dusty season correlate with these orientations furthermore west facing slopes at olympus have a thicker dust cover these observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow the paucity of slope streaks at high latitudes and their preferential orientation on south facing slopes have been presented as an evidence for a potential role of h 2 o phase transition in triggering or flow the potential role of h 2 o cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations the role of h 2 o might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes 30 n 33 n and on all slopes further north

seasonal erosion and restoration of mars northern polar dunes despite radically different environmental conditions terrestrial and martian dunes bear a strong resemblance indicating that the basic processes of saltation and grainfall sand avalanching down the dune slipface operate on both worlds here we show that martian dunes are subject to an additional modification process not found on earth springtime sublimation of mars co2 seasonal polar caps numerous dunes in mars north polar region have experienced morphological changes within a mars year detected in images acquired by the high resolution imaging science experiment on the mars reconnaissance orbiter dunes show new alcoves gullies and dune apron extension this is followed by remobilization of the fresh deposits by the wind forming ripples and erasing gullies the widespread nature of these rapid changes and the pristine appearance of most dunes in the area implicates active sand transport in the vast polar erg in mars current climate

slope streaks on mars correlations with surface properties and the potential role of water the mars orbiter camera on board the mars global surveyor spacecraft has returned images of numerous dark streaks that are the result of down slope mass movement occurring under present day martian climatic conditions we systematically analyze over 23 000 high resolution images and demonstrate that slope streaks form exclusively in regions of low thermal inertia confirming earlier results steep slopes and remarkably only where peak temperatures exceed 275 k the northernmost streaks which form in the coldest environment form preferentially on warmer south facing slopes repeat images of sites with slope streaks show changes only if the time interval between the two images includes the warm season surprisingly in light of the theoretically short residence time of h 2o close to the surface the data support the possibility that small amounts of water are transiently present in low latitude near surface regions of mars and undergo phase transitions at times of high insolation triggering the observed mass movements

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

topographic measurements of slope streaks on mars abstract slope streaks are enigmatic actively forming albedo features occurring on slopes in high albedo low thermal inertia dust rich equatorial regions on mars they are a specifically martian phenomenon with no direct analogs on the earth their morphology suggests that the streaks are initiated at their upslope tips and propagate down to their termini however the physical mechanism of their formation is uncertain we performed a large series of measurements of slopes associated with slope streaks using stereo pairs of high resolution orbital images obtained by hirise camera and generated several digital elevation models for selected streaks we found that 1 slopes at the upslope streak tips range widely however there is a strong indication that streaks can be initiated only on slopes steeper than 20 2 slopes of the streak termini show an even wider range with some streaks terminating at slopes as steep as their tips while others propagate all the way down to horizontal surfaces 3 the streaks can propagate stably for long many hundreds of meters distances and can turn following the topographic gradient on 10 15 slopes 4 no uphill propagation of streaks is detected over baselines of tens of meters 5 the slope streaks often propagate over 1 2 m high obstacles and can climb 1 2 m uphill over short meters distances we used these findings to assess the viability of two classes of hypotheses about slope streak formation mechanisms proposed earlier 1 dry some kind of run away avalanche like dry granular flow and 2 wet some kind of run away propagation of a front of percolating brines in the shallow subsurface no specific observation unambiguously proves or rejects either of the two mechanisms several of our findings are readily explained by the dry mechanism and cannot be easily explained with any kind of wet mechanism while other findings are closely consistent with the wet mechanism and are difficult to reconcile with the dry mechanism this situation might be explained by equifinality meaning that the streaks despite their similarity are formed by different physical processes alternatively some modifications to either the dry or wet mechanisms may be able to provide a coherent explanation it is also possible that new ideas are needed to understand the processes involved

modification of martian slope streaks by eolian processes recent images from the high resolution imaging science experiment hirise camera have shown that slope streaks have relief on the order of a meter or less this study presents observations of transverse bedforms and infill deposits within slope streak beds that were not previously identified or were uncommon from earlier analyses of hirise images transverse bedforms are linear to slightly arcuate features oriented transverse to the slope streak bed which may be analogous to terrestrial splash or coarse grained ripples based on their morphology wavelength and amplitude in addition to the bedforms there is also evidence that slope streak beds gradually shallow over time by infilling of material the presence of ripples within slope streaks implies that saltation capable material is available on the surface today and or was available in the recent past although airfall dust is not a capable saltation source material aggregates of electrostatically bound dust that are possibly later cemented by salts may serve as a source from the results of this study we hypothesize a sequence of events in a slope streak formation and modification cycle where grains saltate to form ripples along the bed of a slope streak airfall dust mantling causes gradual fading of the streak and infill material buries the ripples eventually reaching the pre avalanche surface that removes all traces of relief

mass movement within a slope streak on mars 1 slope streaks on mars represent a currently active geological process various theories for slope streak formation have suggested that slope streaks form by disturbing only a thin surface veneer or by staining of the surface preserving pre existing topography within the streak theories also vary as to whether the formation mechanism requires the presence of water or another liquid we present observations of a slope streak that reveal topographic mounds within the streak these mounds do not continue outside the streak and we suggest that they formed with or immediately after the slope streak we use estimates of the total volume of mounds in this particular streak compared with the estimated excavation volume to extrapolate to a global sediment transport rate from slope streak formation if this slope streak is typical then this calculated rate is greater than estimates of the total volume of material transported by dust storms each year

sporadic formation of slope streaks on mars abstract slope streaks are a form of gravity driven mass movements that frequently occur on mars today the cause of slope streak formation remains unclear both dry and wet processes have been suggested here we observationally constrain the time of the year during which slope streaks form imagery from four mars orbiting cameras is mined to identify locations that have been imaged repeatedly and the overlapping images are surveyed for streak activity a search algorithm automatically finds the locations on the surface that have been imaged most often based on a graph representation dark slope streaks are found to form sporadically throughout the mars year at one study site in the olympus mons aureole observations constrain slope streak formation to at least five distinct time intervals within a single mars year new slope streaks form spatially isolated or in small groups within a few kilometers of one another the observations suggest that slope streak triggering is unrelated to season and not caused by any large regional events most slope streaks are caused by sporadic events of small spatial extent

slope streak formation and dust deposition rates on mars 1 the mars orbiter camera moc has imaged sometimes repeatedly mass movements known as slope streaks which are abundant in the dust covered regions on mars they are among the few known examples of contemporary surface changes a survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of 7 per existing streak per martian year either there is a complete turnover within a few decades or the streak population is currently increasing rapidly large spatial as well as possible temporal variations in the formation rate are obtained from these data streaks do not appear to fade over time periods comparable to their inverse formation rate of 28 years as seen by analysis of viking orbiter images containing streaks that are still visible in moc images gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate and its current imbalance with the fading rate