viscous flow features on the surface of mars observations from high resolution mars orbiter camera moc images 10 5 10 7 years of the material our shear stress estimates of 10 1 5 10 2 5 mpa yield strain rates on the order of 10 11 10 16 s 1 which are within the superplastic flow regime of ice mean annual surface temperatures age constraints and strain estimates show that it is possible for a meters thick ice dust mixture to undergo viscous deformation under past or present surface conditions for ice grain sizes 10 mm the meters thick layer in which the viscous flow features formed is morphologically similar to a degraded meters thick ice dust surface deposit dissected mantle terrain locations of the viscous flow features dissected mantle terrain and recent gullies are concentrated in the midlatitude regions and all three show identical distributions as a function of latitude with the maximum frequency of occurrence at 40 n and s the strong association between these small scale flow features and the dissected mantle terrain large scale viscous flow features and recent gullies imply that deposition deformation and removal of ice rich materials has played an important role in the modification of the surface in the midlatitudes of mars during the amazonian and possibly longer index terms 5470 planetology solid surface planets surface materials and properties 5416 planetology solid surface planets glaciation 1863 hydrology snow and ice 1827 1823 hydrology frozen ground 8168 tectonophysics stresses general keywords viscous flow viscous creep dissected mantle terrain ice rich deposits mars climate recent gullies

a closer look at water related geologic activity on mars water has supposedly marked the surface of mars and produced characteristic landforms to understand the history of water on mars we take a close look at key locations with the high resolution imaging science experiment on board the mars reconnaissance orbiter reaching fine spatial scales of 25 to 32 centimeters per pixel boulders ranging up to approximately 2 meters in diameter are ubiquitous in the middle to high latitudes which include deposits previously interpreted as finegrained ocean sediments or dusty snow bright gully deposits identify six locations with very recent activity but these lie on steep 20 degrees to 35 degrees slopes where dry mass wasting could occur thus we cannot confirm the reality of ancient oceans or water in active gullies but do see evidence of fluvial modification of geologically recent mid latitude gullies and equatorial impact craters

chloride bearing materials in the southern highlands of mars chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing spectrally distinct surface deposits consistent with chloride bearing materials have been identified and mapped using data from the 2001 mars odyssey thermal emission imaging system these deposits are found throughout regions of low albedo in the southern highlands of mars geomorphologic evidence from orbiting imagery reveals these deposits to be light toned relative to their surroundings and to be polygonally fractured the deposits are small

formation of patterned ground and sublimation till over miocene glacier ice in beacon valley southern victoria land antarctica a thin glacial diamicton informally termed granite drift occupies the floor of central beacon valley in southern victoria land antarctica this drift is 40 ar 39 ar analyses of presumed in situ ash fall deposits that occur within granite drift at odds with the great age of this ice are high centered polygons that cut granite drift if polygon development has reworked and retransported ash fall deposits then they are untenable as chronostratigraphic markers and cannot be used to place a minimum age on the underlying glacier ice our results show that the surface of granite drift is stable at polygon centers and that enclosed ash fall deposits can be used to define the age of underlying glacier ice in our model for patterned ground development active regions lie only above polygon troughs where enhanced sublimation of underlying ice outlines high centered polygons the rate of sublimation is influenced by the development of porous gravel and cobble lag deposits that form above thermal contraction cracks in the underlying ice a negative feedback associated with the development of secondary ice lenses at the base of polygon troughs prevents runaway ice loss secondary ice lenses contrast markedly with glacial ice by lying on a d versus 18 o slope of 5 rather than a precipitation slope of 8 and by possessing a strongly negative deuterium excess the latter indicates that secondary ice lenses likely formed by melting downward percolation and subsequent refreezing of snow trapped preferentially in deep polygon troughs the internal stratigraphy of granite drift is related to the formation of surface polygons and surrounding troughs the drift is composed of two facies a nonweathered matrix supported diamicton that contains 25 striated clasts in the 16 mm fraction and a weathered clast supported diamicton with varnished and wind faceted gravels and cobbles the weathered facies is a coarse grained lag of granite drift that occurs at the base of polygon troughs and in lenses within the nonweathered facies the concentration of cosmogenic 3 he in dolerite cobbles from two profiles through the nonweathered drift facies exhibits steadily decreasing values and shows the drift to have formed by sublimation of underlying ice these profile patterns and the 3 he surface exposure ages of 1 18 0 08 ma and 0 18 0 01 ma atop these profiles indicate that churning of clasts by cryoturbation has not occurred at these sites in at least the past 10 5 and 10 6 yr although granite drift is stable at polygon centers low frequency slump events occur at the margin of active polygons slumping together with weathering of surface clasts creates the large range of cosmogenic nuclide surface exposure ages observed for granite drift maximum rates of sublimation near active thermal contraction cracks calculated by using the two 3 he depth profiles range from 5 m m y to 90 m m y sublimation rates are likely highest immediately following major slump events and decrease thereafter to values well below our maximum estimates nevertheless these rates are orders of magnitude lower than those computed on theoretical grounds during eruptions of the nearby mcmurdo group volcanic centers ash fall debris collects at the surface of granite drift either in open thermal contraction cracks or in deep troughs that lie above contraction cracks these deposits subsequently lower passively as the underlying glacier ice sublimes the fact that some regions of granite drift have escaped modification by patterned ground for at least 8 1 ma indicates long term geomorphic stability of individual polygons once established polygon toughs likely persist for as long as 10 5 10 6 yr our model of patterned ground formation which applies to the hyperarid cold desert polar climate of antarctica may also apply to similar sized polygons on mars that occur over buried ice in utopia planitia

neoproterozoic sand wedges crack formation in frozen soils under diurnal forcing during a snowball earth thermal contraction cracking of permafrost produced sand wedge polygons at sea level on the paleo equator during late neoproterozoic glacial episodes these sand wedges have been used as evidence for high v 54 paleoobliquity of the earth s ecliptic because cracks that form wedges are hypothesized to require deep seasonal cooling so the depth of the stressed layer in the ground reaches v 1 m similar to the measured depths of cracks that form wedges to test the counter hypothesis that equatorial cracks opened under a climate characterized by a strong diurnal cycle and low mean annual temperature snowball earth conditions we examine crack formation in frozen ground subject to periodic temperature variations we derive analytical expressions relating the newtonian viscosity to the potential crack depth concluding that cracks will form only in frozen soils with viscosities greater than v10 14 pa s we also show numerical calculations of crack growth in frozen soils with stress and temperature dependent rheologies and find that fractures may propagate to depths 3 25 times the depth of the thermally stressed layer in equatorial permafrost during a snowball earth because the mean annual temperature is low enough to keep the ground cold and brittle to relatively great depths 9 2002 elsevier science b v all rights reserved

martian gullies in the southern mid latitudes of mars evidence for climate controlled formation of young fluvial features based upon local and global topography a new survey of mars orbiter camera moc narrow angle images of gullies in the 30 45 s latitude band includes their distribution morphology local topographic setting orientation elevation and slopes these new data show that gully formation is favored over a specific range of conditions elevation 5000 to 3000 m slope 10 and orientation 83 8 on pole facing slopes these data and the frequent occurrence of gullies on isolated topographic highs lead us to support the conclusion that climatic related processes of volatile accumulation and melting driven by orbital variations are the most likely candidate for processes responsible for the geologically recent formation of martian gullies

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars the antarctic dry valleys adv are generally classified as a hyper arid cold polar desert the region has long been considered an important terrestrial analog for mars because of its generally cold and dry climate and because it contains a suite of landforms at macro meso and microscales that closely resemble those occurring on the martian surface the extreme hyperaridity of both mars and the adv has focused attention on the importance of salts and brines on soil development phase transitions from liquid water to water ice and ultimately on process geomorphology and landscape evolution at a range of scales on both planets the adv can be subdivided into three microclimate zones a coastal thaw zone an inland mixed zone and a stable upland zone zones are defined on the basis of summertime measurements of atmospheric temperature soil moisture and relative humidity subtle variations in these climate parameters result in considerable differences in the distribution and morphology of 1 macroscale features e g slopes and gullies 2 mesoscale features e g polygons including ice wedge sand wedge and sublimation type polygons as well as viscous flow features including solifluction lobes gelifluction lobes and debris covered glaciers and 3 microscale features e g rock weathering processes features including salt weathering wind erosion and surface pitting equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones some equilibrium landforms such as sublimation polygons indicate the presence of extensive near surface ice identification of similar landforms on mars may also provide a basis for detecting the location of shallow ice landforms that today appear in disequilibrium with local microclimate conditions in the adv signify past and or ongoing shifts in climate zonation understanding these shifts is assisting in the documentation of the climate record for the adv a similar type of landform analysis can be applied to the surface of mars where analogous microclimates and equilibrium landforms occur 1 in a variety of local environments 2 in different latitudinal bands and 3 in units of different ages documenting the nature and evolution of the adv microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on mars

identification of sublimation type thermal contraction crack polygons at the proposed nasa phoenix landing site implications for substrate properties and climate driven morphological evolution 1 we identify a surface within the nasa phoenix landing site area d characterized by boulder topped polygonally patterned mounds comparable in radius and cross sectional morphology to terrestrial sublimation polygons found in antarctica both martian and antarctic polygons display topographic asymmetry with shallow equator facing slopes and steep pole facing slopes interpreted to indicate insolation dependent differential sublimation of buried ice on the basis of morphological similarities we classify the phoenix box 1 polygons as sublimation polygons terrestrial sublimation polygons form where ice volumes exceeding available pore space occur in the shallow subsurface and where near surface conditions are too cold and dry to permit the development of saturated active layers conditions comparable to those recently modeled for mars in the phoenix landing site area d box 1 the identification of sublimation polygons on mars would provide direct evidence for shallow ground ice exceeding pore ice volumes and shed light on the emplacement mechanism of this ice

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

formation of gullies on mars link to recent climate history and insolation microenvironments implicate surface water flow origin features seen in portions of a typical midlatitude martian impact crater show that gully formation follows a geologically recent period of midlatitude glaciation geological evidence indicates that in the relatively recent past sufficient snow and ice accumulated on the pole facing crater wall to cause glacial flow and filling of the crater floor with debris covered glaciers as glaciation waned debris covered glaciers ceased flowing accumulation zones lost ice and newly exposed wall alcoves continued as the location for limited snow frost deposition entrapment and preservation analysis of the insolation geometry of this pole facing crater wall and similar occurrences in other craters at these latitudes on mars shows that they are uniquely favored for accumulation of snow and ice and a relatively more rapid exposure to warmer summer temperatures we show that after the last glaciation melting of residual snow and ice in alcoves could have formed the fluvial channels and sedimentary fans of the gullies recent modeling shows that top down melting can occur in these microenvironments under conditions similar to those currently observed on mars if small amounts of snow or frost accumulate in alcoves and channels accumulation and melting is even more favored in the somewhat wetter relatively recent geological past of mars after the period of active glaciation

northern hemisphere martian gullies and mantled terrain implications for near surface water migration in mars recent past 1 we report on a systematic study of gullies and mantled terrain in the northern hemisphere of mars consistent with previous work the mantled terrain is generally located on poleward facing slopes and gullies are found at all orientations new results are as follows 1 the range of orientations of mantled terrain increases toward the pole 2 near polar gullies are commonly less morphologically developed compared to ones in the temperate latitudes 3 gullies toward the pole are better preserved than those closer to the equator and 4 these studies are conducted in the northern hemisphere whereas most previous work investigated the south no gully model in the literature cleanly fits all these observations nor any other gully observations reported in other papers however the likely effects of obliquity and precession variations on snow formation preservation and melting are consistent with many of the results

the interior and orbital evolution of charon as preserved in its geologic record abstract pluto and its largest satellite charon currently orbit in a mutually synchronous state both bodies continuously show the same face to one another this orbital configuration is a natural end state for bodies that have undergone tidal dissipation in order to achieve this state both bodies would have experienced tidal heating and stress with the extent of tidal activity controlled by the orbital evolution of pluto and charon and by the interior structure and rheology of each body as the secondary charon would have experienced a larger tidal response than pluto which may have manifested as observable tectonism unfortunately there are few constraints on the interiors of pluto and charon in addition the pathway by which charon came to occupy its present orbital state is uncertain if charon s orbit experienced a high eccentricity phase as suggested by some orbital evolution models tidal effects would have likely been more significant therefore we determine the conditions under which charon could have experienced tidally driven geologic activity and the extent to which upcoming new horizons spacecraft observations could be used to constrain charon s internal structure and orbital evolution using plausible interior structure models that include an ocean layer we find that tidally driven tensile fractures would likely have formed on charon if its eccentricity were on the order of 0 01 especially if charon were orbiting closer to pluto than at present such fractures could display a variety of azimuths near the equator and near the poles with the range of azimuths in a given region dependent on longitude east west trending fractures should dominate at mid latitudes the fracture patterns we predict indicate that charon s surface geology could provide constraints on the thickness and viscosity of charon s ice shell at the time of fracture formation

geologically recent gully polygon relationships on mars insights from the antarctic dry valleys on the roles of permafrost microclimates and water sources for surface flow we describe the morphology and spatial relationships between composite wedge polygons and mars like gullies consisting of alcoves channels and fans in the hyper arid antarctic dry valleys adv as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground gullies in the adv arise in part from the melting of atmospherically derived wind blown snow trapped in polygon troughs snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions ice cemented permafrost provides an impermeable substrate over which meltwater flows but does not significantly contribute to meltwater generation relationships between contraction crack polygons and sedimentary fans at the distal ends of gullies show deposition of fan material in polygon troughs and dissection of fans by expanding polygon troughs these observations suggest the continuous presence of meters thick ice cemented permafrost beneath adv gullies we document strong morphological similarities between gullies and polygons on mars and those observed in the adv inland mixed microclimate zone on the basis of this morphological comparison we propose an analogous top down melting model for the initiation and evolution of martian gullies that occur on polygonally patterned mantled surfaces

the role of arcuate ridges and gullies in the degradation of craters in the newton basin region of mars abstract a survey of craters in the vicinity of newton basin using high resolution images from mars global surveyor and mars odyssey was conducted to find and analyze examples of gullies and arcuate ridges and assess their implications for impact crater degradation processes in the phaethontis quadrangle mc 24 we identified 225 craters that contain these features of these 188 had gullies on some portion of their walls 118 had arcuate ridges at the bases of the crater walls and 104 contained both features typically on the same crater wall a major result is that the pole facing or equator facing orientation of these features is latitude dependent at latitudes 44 s equator facing orientations for both ridges and gullies are prevalent but at latitudes

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

mars orbiter laser altimeter pulse width measurements and footprint scale roughness the mars orbiter laser altimeter mola measured the pulse width and energy of altimetric laser returns during the course of two mars years of operations as secondary science objectives mola obtains the footprint scale roughness and the bidirectional reflectivity of mars mola underwent extensive preflight calibration and pulse measurements were monitored continuously in flight but anomalous values of roughness have been inferred a calibration of pulse widths using inflight data yields a slope corrected roughness over 75 m diameter footprints that may be used for quantitative geomorphic surface characterization required for example for landing site selection the recalibration uses a total least squares estimation of pulse characteristics that generalizes the method of abshire et al 2000 this method utilizing the timing at voltage threshold crossings and the area between crossings accounts for observation errors and shows that surface roughness as small as 1 m can be resolved

spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on mars 1 patterned grounds like polygonal features are the signature of climatic effects in periglacial regions on earth identifying similar features on mars is important for an understanding of the past martian climate in this study we mapped fresh patterned landforms from the systematic analysis of mars orbiter camera high resolution images we show that most of them are distributed at latitudes poleward of 55 making a climatic control likely this distribution correlates to the distribution of ground ice detected by the neutron spectrometer aboard mars odyssey this correlation is likely the consequence of the neutron spectrometer detecting ice no deeper than about 1 m patterned ground formation requires ice in this range of depth because these features are triggered by the propagation of a thermal wave that is driven by seasonal or diurnal changes in insolation which affect the temperature in the uppermost ground layers sublimation seems to play a role in the shaping of many of the small patterns observed at latitudes between 55 and 70 no widespread polygonal features are correlated to the equatorial regions where hydrogen is detected by the neutron spectrometer

mars nature and evolution of young latitude dependent water ice rich mantle 1 high resolution altimetry and imaging have revealed the presence of a meters thick sedimentary layer at middle to high northern and southern latitudes presently covering at least 23 of the planet the layer is interpreted to be water ice rich and to undergone degradation recently its activity very likely coincided with the last major obliquity excursion a few hundred thousand years ago the majority of the layer at higher latitudes however persisted for a much longer time in the late amazonian stratigraphic analysis suggests a complex history of successive episodes of deposition and removal repeated deposition and removal of the mantles are interpreted to be responsible for the unusual statistical properties of kilometer scale topography in the transitional mid latitude zones

observations of martian gullies and constraints on potential formation mechanisms ii the northern hemisphere abstract the formation process es responsible for creating the observed geologically recent gully features on mars has remained the subject of intense debate since their discovery we present new data and analysis of northern hemisphere gullies from mars global surveyor data which is used to test the various proposed mechanisms of gully formation we located 137 mars orbiter camera moc images in the northern hemisphere that contain clear evidence of gully landforms and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures northern hemisphere gullies are clustered in arcadia planitia tempe terra acidalia planitia and utopia planitia these gullies form in craters 84 knobby terrain 4 valleys 3 other unknown terrains 9 and are found on all slope orientations although the majority of gullies are equator facing most gullies 63 are associated with competent rock strata 26 are not associated with strata and 11 are ambiguous assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 95 of the gully alcove bases with adequate data coverage lie at depths where subsurface temperatures are greater than 273 k and 5 of the alcove bases lie within the solid water regime the average alcove length is 470 m and the average channel length is 690 m based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies these findings gleaned from the northern hemisphere data are in general agreement with analyses of gullies in the southern hemisphere heldmann j l mellon m t 2004 icarus 168 285 304

absolute dune ages and implications for the time of formation of gullies in nirgal vallis mars 1 transverse dunes cover the valley floor of nirgal vallis a 670 km long valley network at 318 e and 29 s the dunes are superposed by small undeformed impact craters which implies that the dunes are inactive under present atmospheric conditions the last active phase of dune movement absolute age can be determined by crater size frequency distributions the derived absolute ages from high resolution mars global surveyor mars orbiter camera imagery range from approximately 300 000 years to 1 4 myr b p error of factor of 2 the dunes are also superposed by gully deposits aprons which implies a younger age of the gullies these superposition relationships show that the gullies in this midlatitude region are at the most 3 myr old but might be even younger than 300 000 years

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

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

orientation and distribution of recent gullies in the southern hemisphere of mars observations from high resolution stereo camera mars express hrsc mex and mars orbiter camera mars global surveyor moc mgs data 1 geologically recent small gullies on mars display morphologies consistent with erosion by water or by debris flows suggested formation models are divided into two main categories 1 groundwater or 2 melting of near surface ice snow sourced from the atmosphere we have measured location and orientation and recorded the local contexts of gullies to constrain the likely models of gully formation more than 22 000 mars orbiter camera narrow angle moc na and 120 mars express high resolution stereo camera hrsc images in the southern hemisphere were searched for gullies discrete gullied slope sections with consistent orientation were recorded rather than individual gullies slope setting impact crater valley wall etc location and orientation were recorded for each slope section more than 750 moc images with gullies 900 distinct gullied slope sections and more than 40 hrsc images 380 distinct gullied slope sections were identified from both moc and hrsc gullies were found to be most common between 30 and 50 degrees latitude and to have an overall pole facing preference the preferred gully orientation for hrsc is southeast rather than south in moc owing to illumination effects that make gullies difficult to detect on south to southwest facing slopes in hrsc in both moc and hrsc surveys higher latitude gullies show less preference for pole facing than those at mid latitudes both data sets produced similar results demonstrating that our data are reliable we suggest that the observed latitudinal and orientation distributions of gullies show that insolation and atmospheric conditions play a key role in gully formation

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

observations of martian gullies and constraints on potential formation mechanisms abstract the discovery of presumably geologically recent gully features on mars malin and edgett 2000 science 288 2330 2335 has spawned a wide variety of proposed theories of their origin including hypotheses of the type of erosive material to test the validity of gully formation mechanisms data from the mars global surveyor spacecraft has been analyzed to uncover trends in the dimensional and physical properties of the gullies and their surrounding terrain we located 106 mars orbiter camera moc images that contain clear evidence of gully landforms distributed in the southern mid and high latitudes and analyzed these images in combination with mars orbiter laser altimeter mola and thermal emission spectrometer tes data to provide quantitative measurements of numerous gully characteristics parameters we measured include apparent source depth and distribution vertical and horizontal dimensions slopes orientations and present day characteristics that affect local ground temperatures we find that the number of gully systems normalized to the number of moc images steadily declines as one moves poleward of 30 s reaches a minimum value between 60 63 s and then again rises poleward of 63 s all gully alcove heads occur within the upper one third of the slope encompassing the gully and the alcove bases occur within the upper two thirds of the slope also the gully alcove heads occur typically within the first 200 meters of the overlying ridge with the exception of gullies equatorward of 40 s where some alcove heads reach a maximum depth of 1000 meters while gullies exhibit complex slope orientation trends gullies are found on all slope orientations at all the latitudes studied assuming thermal conductivities derived from tes measurements as well as modeled surface temperatures we find that 79 of the gully alcove bases lie at depths where subsurface temperatures are greater than 273 k and 21 of the alcove bases lie within the solid water regime most of the gully alcoves lie outside the temperature pressure phase stability of liquid co2 based on a comparison of measured gully features with predictions from the various models of gully formation we find that models involving carbon dioxide melting ground ice in the upper few meters of the soil dry landslide and surface snowmelt are the least likely to describe the formation of the martian gullies although some discrepancies still exist between prediction and observation the shallow and deep aquifer models remain as the most plausible theories interior processes involving subsurface fluid sources are generally favored over exogenic processes such as wind and snowfall for explaining the origin of the martian gullies

recent bright gully deposits on mars wet or dry flow bright gully sediments attributed to liquid water flow have been deposited on mars within the past several years to test the liquid water flow hypothesis we constructed a high resolution 1 m pixel photogrammetric digital elevation model of a crater in the centauri montes region where a bright gully deposit formed between 2001 and 2005 we conducted one dimensional 1 d and 2 d numerical flow modeling to test whether the deposit morphology is most consistent with liquid water or dry granular flow liquid water flow models that incorporate freezing can match the runout distance of the flow for certain freezing rates but fail to reconstruct the distributary lobe morphology of the distal end of the deposit dry granular flow models can match both the observed runout distance and the distal morphology wet debris flows with high sediment concentrations are also consistent with the observed morphology because their rheologies are often similar to that of dry granular flows as such the presence of liquid water in this flow event cannot be ruled out but the available evidence is consistent with dry landsliding

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

structural evolution of gavilgarh tan shear zone central india a possible case of partitioned transpression during mesoproterozoic oblique collision within central indian tectonic zone abstract gavilgarh tan shear zone gtsz a map scale ductile shear zone occurring in the southern part of the central indian tectonic zone citz contains many important clues to the tectonics of this important proterozoic mobile belt of central india which is yet controversial and hotly debated data from structural mapping microstructural study and kinematic analyses of the gtsz have been presented in this paper which clearly implies that gtsz is mainly represented by a wrench dominated transpressional shear zone with sinistral shear sense analysis of lineation patterns shows that while horizontal stretching dominated within the ductile shear zone rocks on either side north and south of it stretched vertically with a transition zone of simultaneous horizontal and vertical stretching in between these two domains a general transpressional strain has thus been partitioned into wrench and pure shear dominated domains at large scale further strain partitioning also took place at the outcrop scale geochemistry of the granitoids occupying the shear zone and its surrounding area indicates continental collision set up which supports the structural model on the basis of earlier proposed tectonic models and limited geochronological data available of the southern part of citz it is suggested here that an oblique collision and final suturing between the northern bundelkhand craton and southern bastar craton terrains within the citz around 1100 ma have been partly accommodated by partitioned transpression along gtsz and its surrounding gneiss granitoid terrain more intensive geochronological constraint of the collision event from both northern and southern side are however lacking at present

geologic settings of martian gullies implications for their origins 1 martian gullies are found on steep slopes of all origins on all sorts of terrains of all ages scattered across nearly all of mars gullies are observed on all manner of substrates layered massive shattered rubble with or without nearby mantling deposits gullies are most common in the southern midlatitudes but also occur in the northern hemisphere in near polar terrain on equatorial volcanoes and on northern plains most gullies in the southern hemisphere are on south facing slopes but they occur on slopes of all orientations gullies are among the youngest features on mars but locally are overlain by eolian deposits and cut by faults old or eroded gullies are rare and those found have been partially stripped from slopes leaving no rock debris behind most gully deposits contain no detectable rocks these data are inconsistent with published hypotheses of gully formation including seeps and breakouts of water or brine hydrothermal activity cryovolcanism and breakouts from liquid carbon dioxide the data are consistent with gullies being dry flows of eolian material dust and silt comparable to climax snow avalanches on earth eolian sedimentation should be correlated little with underlying geology cause of slope age of terrain type of terrain or the nature of the rocks eolian sedimentation should be correlated with wind deceleration which will cause suspended sediment to drop and areas with common gullies are those with strong wind deceleration predicted by global circulation model in such areas sediment will be deposited preferentially in the lee of obstacles for the gully rich areas of the southern midlatitudes winds blow from the nnw so that sediment is deposited on sse facing slopes i e poleward these predictions are in accord with observations