observations of periglacial landforms in utopia planitia with the high resolution imaging science experiment hirise 1 the region of western utopia planitia 80 105 e 40 55 n displays several types of landforms similar to earth periglacial features including scallop shaped depressions and networks of polygonal terrains the scalloped depressions have been proposed to originate from thermokarstic processes such as sublimation and or melting of near surface ground ice using hirise imagery we characterize these depressions and several associated distinct polygon networks in unprecedented morphologic and topographic detail and investigate support for an ice based degradation process the scalloped depressions and interior polygons and ridges are found to evolve together mainly influenced by sublimation local proximity of ground ice to the surface and obliquity variations

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

lineated valley fill lvf and lobate debris aprons lda in the deuteronilus mensae northern dichotomy boundary region mars constraints on the extent age and episodicity of amazonian glacial events abstract in order to assess the nature degradational processes and history of the dichotomy boundary on mars we conducted a detailed morphological analysis of a 70 000 km 2 region of its northern portion north central deuteronilus mensae south of lyot in the vicinity of sinton crater this region is characterized by the distinctive sinuous 2 km high plateau scarp boundary outlying massifs to the north and extensive fretted valleys dissecting the plateau to the south these features represent the first order modification and retreat of the dichotomy boundary and are further modified by processes that form lineated valley fill lvf in the fretted valleys and lobate debris aprons lda along the dichotomy scarp and surrounding the outlying massifs we use new high resolution image and topography data to examine the nature and origin of lvf and lda and to investigate the climatic and accompanying degradational history of the escarpment on the basis of our analysis we conclude that 1 lvf and lda deposits within the study region are comprised of the same material show integrated flow patterns and originate as debris covered valley glaciers a significant amount of ice hundreds of meters is likely to remain today beneath a thin cover of sublimation till 2 there is depositional evidence to suggest glacial highstands at least 800 m above the present level implying previous conditions in which the distribution of ice was much more widespread this is supported by similar deposits within many other areas across the dichotomy boundary 3 the timing of the most recent large scale activity of the lda lvf in this area is about 100 500 million years ago similar to ages reported elsewhere along the dichotomy boundary 4 there is evidence for a secondary but significantly limited phase of glaciation the deposits of which are limited to the vicinity of the alcoves similar later phases have also been reported elsewhere along the dichotomy boundary 5 modification of the fretted valleys of the dichotomy boundary has been substantial locally but we find no evidence that the amazonian glacial epochs caused retreat of the dichotomy boundary of the scale of tens to hundreds of kilometers our findings support the results of an analysis just to the east of the study region and of studies carried out elsewhere along the dichotomy boundary that find further evidence for the remnants of debris covered glaciers and extensive valley glacial land systems

pedestal crater heights on mars a proxy for the thicknesses of past ice rich amazonian deposits abstract mid latitude pedestal craters on mars offer crucial insights into the timing and extent of widespread ice rich deposits during the amazonian period our previous comprehensive analysis of pedestal craters strongly supports a climate related formation mechanism whereby pedestals result from impacts into ice rich material at mid latitudes during periods of higher obliquity the ice from this target deposit later sublimates due to obliquity changes but is preserved beneath the protective cover of the armored pedestal as such the heights of pedestals act as a proxy for the thicknesses of the paleodeposits in this analysis our measurement of 2300 pedestal heights shows that although pedestals can reach up to 260 m in height 82 are shorter than 60 m and only 2 are taller than 100 m mean pedestal heights are 48 0 m in the northern mid latitudes and 40 4 m in the southern mid latitudes with the tallest pedestals located in utopia planitia acidalia planitia and malea planum we use these data in conjunction with prior climate model results to identify both regional and global trends regarding ice accumulation during obliquity excursions our data provide evidence for multiple episodes of emplacement and removal of the mid latitude ice rich deposit based on stratigraphic relationships between pedestal craters and the close proximity of pedestals with significantly different heights

concentric crater fill in utopia planitia history and interaction between glacial brain terrain and periglacial mantle processes abstract at martian mid to high latitudes the surfaces of potentially ice rich features including concentric crater fill lobate debris aprons and lineated valley fill typically display a complex texture known as brain terrain due to its resemblance to the complex patterns on brain surfaces in order to determine the structure and developmental history of concentric crater fill and overlying latitude dependent mantle ldm material brain terrain and polygonally patterned ldm surfaces are analyzed using hirise images from four craters in utopia planitia containing concentric crater fill brain terrain and mantle surface textures are classified based on morphological characteristics 1 closed cell brain terrain 2 open cell brain terrain 3 high center mantle polygons and 4 low center mantle polygons a combined glacial and thermal contraction cracking model is proposed for the formation and modification of the brain terrain texture of concentric crater fill a similar model related to thermal contraction cracking and differential sublimation of underlying ice is proposed for the formation and development of polygonally patterned mantle material both models require atmospheric deposition of ice likely during periods of high obliquity but do not require wet active layer processes crater dating of brain terrain and mantled surfaces suggests a transition at martian mid latitudes from peak glacial conditions occurring within the past 10 100 my to a quiescent period followed by a cold desert periglacial period during the past 1 2 my

concentric crater fill in the northern mid latitudes of mars formation processes and relationships to similar landforms of glacial origin abstract hypotheses accounting for the formation of concentric crater fill ccf on mars range from ice free processes e g aeolian fill to ice assisted talus creep to debris covered glaciers based on analysis of new ctx and hirise data we find that concentric crater fill ccf is a significant component of amazonian aged glacial landsystems on mars we present mapping results documenting the nature and extent of ccf along the martian dichotomy boundary over 30 to 90 e latitude and 20 80 n longitude on the basis of morphological analysis we classify ccf landforms into classic ccf and low definition ccf classic ccf is most typical in the middle latitudes of the analysis area 30 50 n while a range of degradation processes results in the presence of low definition ccf landforms at higher and lower latitudes we evaluate formation mechanisms for ccf on the basis of morphological and topographic analyses and interpret the landforms to be relict debris covered glaciers rather than ice mobilized talus or aeolian units we examine filled crater depth diameter ratios and conclude that in many locations hundreds of meters of ice may still be present under desiccated surficial debris this conclusion is consistent with the abundance of ring mold craters on ccf surfaces that suggest the presence of near surface ice analysis of breached craters and distal glacial deposits suggests that in some locations ccf related ice was once several hundred meters higher than its current level and has sublimated significantly during the most recent amazonian crater counts on ejecta blankets of filled and unfilled craters suggests that ccf formed most recently between 60 and 300 ma consistent with the formation ages of other martian debris covered glacial landforms such as lineated valley fill lvf and lobate debris aprons lda morphological analysis of ccf in the vicinity of lvf and lda suggests that ccf is a part of an integrated lvf lda ccf glacial landsystem instances of morphological continuity between ccf lvf and lda are abundant the presence of formerly more abundant ccf ice coupled with the integration of ccf into lvf and lda suggests the possibility that ccf represents one component of the significant amazonian mid latitude glaciation s on mars

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

modification of the dichotomy boundary on mars by amazonian mid latitude regional glaciation 1 restoration of the dichotomy boundary to its original position to assess its origin requires a thorough knowledge of processes responsible for its degradation and retreat the unique fretted terrain located along the deuteronilus protonilus mensae northern mid latitude portion of the boundary has been long held to provide clues to dichotomy degradation processes we use new spacecraft data to show that fretted valleys display a multitude of characteristics typical of integrated valley glacial systems on earth multiple theater headed alcove like accumulation areas sharp arete like ridges typical of glacial erosion converging patterns of downslope valley flow valley lineation patterns typical of folding and shear wrap around features indicative of flow around obstacles and broad piedmont like lobes as the valley fill extends out into the northern lowlands the single integrated system containing these features covers about 30 000 km2 and is one of dozens of fretted valleys along the dichotomy boundary in this region these relationships suggest that the boundary area was subjected to very large scale regional glaciation during the amazonian recognition and documentation of this important late stage process provides information critical to reconstructing the original dichotomy boundary

origin of martian northern hemisphere mid latitude lobate debris aprons lobate debris aprons in the martian mid to high latitudes northern and southern hemispheres have been interpreted as ice related features that indicate periglacial climate conditions as recently as late amazonian using mola topographic profiles perpendicular to apron flow fronts we surveyed 36 debris aprons in the northern hemisphere found in the regions of mareotis protonilus and deuteronilus mensae and acheron fossae the profiles of these aprons were compared with idealized simple plastic and viscous power law models for ice rock mixtures all aprons studied exhibit convex profiles similar to a simple plastic model this confirms previous interpretations that debris aprons are ice rich mixtures with rheologies similar to stagnant ice sheets thus indicating high ice concentrations 40 by volume about 60 of the surveyed debris apron population significantly deviates from the idealized simple plastic model profile this may be due to locally reduced ice content which primarily controls apron topography although post emplacement modification due to near surface ice sublimation plays a secondary role in defining the overall shape of aprons it causes conspicuous surface textures degradation by ice sublimation probably results in pitted and ridge and furrow surface textures revealed by high resolution moc images such textures may indicate decreased near surface ice stability since the formation of the aprons possibly due to mars current low obliquity after their emplacement high ice content inferred from topography suggests some debris aprons have ice cores potentially exploitable water resources for future robotic human operations that could prove invaluable for missions remote from polar regions

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

preservation of layered paleodeposits in high latitude pedestal craters on mars an outstanding question in mars climate history is whether or not pedestal craters represent the armored remnants of ice rich paleodeposits we address this question using new high resolution images in a survey of several hundred high latitude pedestal craters we have identified 12 examples in which visible and or topographically expressed layers are exposed on the marginal scarp of the pedestal one example located on the south polar layered deposits preserves ice rich layers that have otherwise been completely removed from the polar cap these observations provide empirical evidence that the pedestal crater formation mechanism is capable of armoring and preserving ice rich layered paleodeposits although layered exposures have not yet been observed in mid latitude pedestal craters high latitude instances of discontinuous partially covered layers suggest that layers can be readily concealed likely through mantling and or mass wasting processes along the marginal scarp this interpretation is supported by the observation that high latitude pedestals with exposed layers along their margins are on average taller than mid latitude examples and have larger steeper marginal scarps which may help to maintain layer exposures these observations favor the interpretation that mid to high latitude pedestal craters represent the armored remnants of ice and dust rich paleodeposits which occurred transiently due to changes in the climate regime preservation of fine scale layering of ice and dust at these latitudes implies that the climate change did not involve regional melting conditions

the dispersal of pyroclasts from ancient explosive volcanoes on mars implications for the friable layered deposits a number of voluminous fine grained friable deposits have been mapped on mars the modes of origin for these deposits are debated the feasibility for an origin by volcanic airfall for the friable deposits is tested using a global circulation model to simulate the dispersal of pyroclasts from candidate source volcanoes near each deposit it is concluded that the medusae fossae formation and electris deposits are easily formed through volcanic processes and that the hellas deposits and south polar pitted deposits could have some contribution from volcanic sources in specific atmospheric regimes the arabia and argyre deposits are not well replicated by modeled pyroclast dispersal suggesting that these deposits were most likely emplaced by other means

mars global surveyor observations of martian fretted terrain the martian fretted terrain between latitudes 30 and 50 n and between 315 and 360 w has been reexamined in light of new mars orbiter camera moc and mars orbiter laser altimeter mola data from mars global surveyor much of the terrain in the 30 50 latitude belt in both hemispheres has a characteristic stippled or pitted texture at moc 1 5 m scale the texture appears to result from partial removal of a formerly smooth thin deposit as a result of sublimation and deflation a complex history of deposition and exhumation is indicated by remnants of a former thicker cover of layered deposits in some hollows and on some slopes particularly those facing the pole are smooth textured deposits outlined by an outward facing escarpment throughout the study area are numerous escarpments with debris flows at their base the escarpments typically have slopes in the 20 30 range at the base of the escarpment is commonly a deposit with striae oriented at right angles to the escarpment outside this deposit is the main debris apron with a surface that typically slopes 2 3 and complex surface textures suggestive of compression sublimation and deflation the presence of undeformed impact craters indicates that the debris flows are no longer forming fretted valleys contain lineated fill and are poorly graded they likely form from fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass wasting processes that formed the debris aprons slope reversals indicate that downvalley flow of the lineated fill is minor the ubiquitous presence of breaks in slope formed by mass wasting and the complex surface textures that result from mass wasting deflation and sublimation decreases the recognizability of the shorelines formerly proposed for this area

geomorphic analysis of lobate debris aprons on mars at mars orbiter camera scale evidence for ice sublimation initiated by fractures 1 lobate debris aprons known to be geomorphic landform indicators of the presence of ground ice are of special interest for future missions devoted to the research of water on mars lobate debris aprons in fretted terrains of deuteronilus and protonilus mensae 35 50 n show typical convex shapes interpreted to be the result of viscous deformation at the scale of mars orbiter camera moc high resolution images the surface of these debris aprons shows complex patterns with small pits and buttes these patterns can be explained by the mantling of dust the accumulation of interstitial ice and the subsequent removal of ice by sublimation the sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures theoretical quantification of sublimation rates therefore minimizes sublimation which is not a homogeneous process at least over the landforms studied crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past in the point of view of future searching of subsurface ice only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform the geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations especially in order to measure current sublimation of ground ice

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

supraglacial and proglacial valleys on amazonian mars abundant evidence exists for glaciation being an important geomorphic process in the mid latitude regions of both hemispheres of mars as well as in specific environments at near equatorial latitudes such as along the western flanks of the major tharsis volcanoes detailed analyses of glacial landforms lobate debris aprons lineated valley fill concentric crater fill viscous flow features have suggested that this glaciation was predominantly cold based this is consistent with the view that the amazonian has been continuously cold and dry similar to conditions today we present new data based on a survey of images from the context camera ctx on the mars reconnaissance orbiter that some of these glaciers experienced limited surface melting leading to the formation of small glaciofluvial valleys some of these valleys show evidence for proglacial erosion eroding the region immediately in front of or adjacent to a glacier while others are supraglacial eroding a glacier s surface these valleys formed during the amazonian consistent with the inferred timing of glacial features based on both crater counts and stratigraphic constraints the small scale of the features interpreted to be of glaciofluvial origin hindered earlier recognition although their scale is similar to glaciofluvial counterparts on earth these valleys appear qualitatively different from valley networks formed in the noachian which can be much longer and often formed integrated networks and large lakes the valleys we describe here are also morphologically distinct from gullies which are very recent fluvial landforms formed during the last several million years and on much steeper slopes 20 30 for gullies versus 10 for the valleys we describe these small valleys represent a distinct class of fluvial features on the surface of mars glaciofluvial their presence shows that the hydrology of amazonian mars is more diverse than previously thought

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

hemispheres apart the crustal dichotomy on mars the hemispheric dichotomy is a fundamental feature of mars expressed by a physiographic and geologic divide between the heavily cratered southern highlands and the relatively smooth plains of the northern lowlands the origin of the dichotomy which may have set the course for most of the subsequent geologic evolution of mars remains unclear internally driven models for the dichotomy form the lowlands by mantle convection plate tectonics or early mantle overturn externally driven models invoke one giant impact or multiple impacts areal densities of buried basins expressed by quasicircular depressions and subsurface echoes in radar sounding data suggest that the dichotomy formed early in the geologic evolution of mars tectonic features along the dichotomy boundary suggest late stage modification by flexure or relaxation of the highlands after volcanic resurfacing of the northern lowlands subsequent deposition and erosion by fluvial aeolian and glacial processes shaped the present day dichotomy boundary

the early martian evolution constraints from basin formation ages impact basin formation ages give insight into the early evolution of a planet the martian basins hellas isidis and argyre provide an important time marker for the cessation of the magnetic dynamo and the crustal thickness distribution both established before 4 ga ago no martian surfaces are older than 4 15 ga based on crater count statistics and all are younger than the oldest lunar ones i show that the heavy bombardment period on the moon and mars evolved similarly but endogenic processes have removed the oldest martian basin record the basin forming projectile population appears to be different from the impactor population observed today in the inner solar system it is yet uncertain whether the heavy bombardment period is cataclysmic or characterized by the decaying flux of planetary formation

modeling vapor diffusion within cold and dry supraglacial tills of antarctica implications for the preservation of ancient ice abstract we modeled water vapor diffusion within mullins till a relatively dry supraglacial till in southern victoria land antarctica that rests directly on mullins glacier purportedly one of the oldest alpine glaciers in the world like most supraglacial tills in cold desert environments mullins till contains three characteristic facies a weathered facies representing the oxidation of iron bearing minerals and the physical disintegration of surface rocks a sand wedge facies representing the episodic infill of thermal cracks associated with contraction crack polygons and an underlying fresh facies representing the addition of englacial debris sourced from rockfall as overlying ice sublimes using a one dimensional model for fickian vapor diffusion through porous media we show that the rate of subsurface ice sublimation varies by 5 5 beneath till facies and that over timescales of 10 5 years diffusion through porous sand wedges contributes to the development of deep troughs surrounding high centered polygons applying site specific meteorological data collected over a four year period we show that ice loss at the stagnant terminus of mullins glacier is 6 6 10 5 m a 1 a value that although low and assuming an ice thickness of 150 m is consistent with complete ice loss under current environmental forcing in 2 5 ma our sensitivity tests indicate that the vast majority of sublimation occurs during the summer months calculated summertime losses drop to zero with either a reduction in soil and ice surface temperatures of 6 4 c or an increase in atmospheric relative humidity from 44 to 75 both of which could arise from an increase in cloud cover over mullins glacier sublimation responses to meteorological forcing are not uniform across mullins glacier a summer increase in soil temperature of 2 c results in negligible change in ice sublimation at mullins terminus but a 27 increase in ice loss in upper mullins valley the key factor is the thickness of mullins till which is greater near the glacier terminus for till thicknesses exceeding 25 cm non linear variations in soil temperature result in downward vapor fluxes capable of producing thin cm scale lenses of secondary pore that cap the surface of buried glacier ice this downward vapor flow sourced from modern snowfall and or elevated atmospheric relative humidity is one of the key factors that enable long term preservation of buried glacier ice overall our results highlight the subtle relations among changes in till texture till thickness and meteorological forcing on the rate of subsurface ice loss and provide insight into the plausible range of conditions under which multi million year old ice can exist beneath thin supraglacial tills

sub kilometre intra crater mounds in utopia planitia mars character occurrence and possible formation hypotheses abstract at the middle latitudes of utopia planitia 35 45 n 65 101 e hundreds of small sized mounds located in sub kilometre impact craters dot the landscape their shape varies from circular to crescentic and their height ranges from 10 to 50 m often metre to decametre pitting is observed as is metres thick banding or stratification mound albedo is relatively high i e 0 16 the plain s terrain in the region previously linked to the latitude dependent mantle ldm of ice dust displays pitting and albedo similar to the small intra crater mounds some workers have suggested that the mounds and the plain s terrain share a common ice dust origin if so then scrutinising the mounds could provide analogical insight on the key geological characteristics and spatial distribution of the ldm itself other workers have hypothesised that the mounds are eroded sedimentary landforms or periglacial mounds underlain by a perennial ice core closed system pingos in this article we develop and then discuss each of the three mound hypotheses in a much more substantial manner than has been done hitherto towards this end we use high resolution images present a detailed regional map of mound distribution and establish a regional platform of topographical analysis using mola data superposed on a large scale ctx mosaic although the ice dust hypothesis is consistent with some observations and measurements we find that a loess based sedimentary hypothesis shows greater plausibility of the three hypotheses evaluated the pingo or periglacial one is the weakest

geomorphological evidence of cold based glacier activity in south victoria land antarctica cold based glaciers have long been recognized as capable of covering and protecting landscapes however recent studies of modern cold based glaciers in antarctica show that in some situations erosion deformation and deposition can occur recognizing the dual ability of cold based glaciers to protect and preserve surfaces on the one hand and erode and modify on the other is important for correctly interpreting the often subtle imprint of cold based glaciers on landscapes a range of geomorphological features related to cold based glacier activity has now been documented along with an improved understanding of cold based glacier structure processes and interaction with various substrates collectively this provides an enhanced ability to understand the impact of cold based glaciers on landscapes and reappraise the geomorphological record such insight allows recognition of previously unknown glacial events and better interpretations of the landscape exposure record this is particularly important at the margins of the antarctic ice sheets where past fluctuations in ice sheet volume and its contributions to post glacial sea level rise are poorly constrained this paper reviews the known geomorphological evidence associated with cold based glaciers in the south victoria land region of the transantarctic mountains it aims to provide progress towards a set of criteria for recognizing cold based glacier activity in other regions and to highlight the implications of cold based glacial activity for surface exposure studies and interpreting glacial history cold based glaciers are below pressure melting point throughout and are therefore frozen to the substrate and move primarily by internal deformation drewry 1986 this led to the long standing view that cold based glaciers cannot slide and are thus incapable of erosion and deposition and therefore protect the underlying surface while numerous studies have shown this to be true in many situations recent investigations of modern cold based glaciers have revealed that in some circumstances complex processes operate at subfreezing temperatures in the basal zone and that cold based glaciers can generate a variety of geomorphological features these studies have forced a reappraisal of the geomorphic effectiveness of cold based glaciers and have confirmed that they can both protect and modify landscapes e g fitzsimons 1996 atkins et al 2002 fitzsimons 2003 waller et al 2012 thus the debate has moved on and the challenge now is to understand the full range of processes and products associated with cold based glaciers and the implications for landscape development hambrey fitzsimons 2010 waller et al 2012 recognizing the often subtle features indicative of cold based glacial activity offers the potential to delineate and date previously unknown or poorly constrained glacial events this is particularly relevant for interpreting glacial history and modelling ice sheet reconstructions for example numerous surface exposure dating studies have been carried out on ice marginal landforms with the aim of constraining past variations in the ice sheet volume however many of these studies have produced inconsistent contradictory results including evidence of complex exposure histories suggesting episodes of burial and reworking by cold based ice e g strasky et al 2008 di nicola et al 2009 compared with warm based glaciers there are still relatively few studies of cold based glaciers and significant gaps in our understanding of the processes and products remains in addition lingering misconceptions regarding the geomorphic effectiveness of cold based glaciers and historic use of ambiguous terminology to describe cold based sediments and landforms mean that the evidence and implications of past cold based glacial events have yet to be fully appreciated by the wider geomorphological community this review provides a summary of known geomorphological features associated with cold based glaciers in the south victoria land region of antarctica it aims to provide a basis for recognizing similar features elsewhere and attempts to draw attention to the implications of cold based glacial geomorphology for the correct application of surface exposure dating studies and interpretation of cold based glacial history

evidence for amazonian northern mid latitude regional glacial landsystems on mars glacial flow models using gcm driven climate results and comparisons to geological observations a fretted valley system on mars located at the northern mid latitude dichotomy boundary contains lineated valley fill lvf with extensive flow like features interpreted to be glacial in origin we have modeled this deposit using glacial flow models linked to atmospheric general circulation models gcm for conditions consistent with the deposition of snow and ice in amounts sufficient to explain the interpreted glaciation in the first glacial flow model simulation sources were modeled in the alcoves only and were found to be consistent with the alpine valley glaciation interpretation for various environments of flow in the system these results supported the interpretation of the observed lvf deposits as resulting from initial ice accumulation in the alcoves accompanied by debris cover that led to advancing alpine glacial landsystems to the extent observed today with preservation of their flow texture and the underlying ice during downwasting in the waning stages of glaciation in the second glacial flow model simulation the regional accumulation patterns predicted by a gcm linked to simulation of a glacial period were used this glacial flow model simulation produced a much wider region of thick ice accumulation and significant glaciation on the plateaus and in the regional plains surrounding the dichotomy boundary deglaciation produced decreasing ice thicknesses with flow centered on the fretted valleys as plateaus lost ice scarps and cliffs of the valley and dichotomy boundary walls were exposed providing considerable potential for the production of a rock debris cover that could preserve the underlying ice and the surface flow patterns seen today in this model the lineated valley fill and lobate debris aprons were the product of final retreat and downwasting of a much larger regional glacial landsystem rather than representing the maximum extent of an alpine valley glacial landsystem these results favor the interpretation that periods of mid latitude glaciation were characterized by extensive plateau and plains ice cover rather than being restricted to alcoves and adjacent valleys and that the observed lineated valley fill and lobate debris aprons represent debris covered residual remnants of a once more extensive glaciation 2011 elsevier inc

the resurfacing history of venus constraints from buffered crater densities because of atmospheric shielding and endogenic resurfacing the population of impact craters on venus is small about a thousand and consists of large craters this population has been used in numerous studies with the goal of deciphering the geologic and geodynamic history of venus but the nearly spatially random nature of the crater population has complicated efforts to understand this history here we utilize the recent 1 15 m scale global geological map of venus ivanov m a head j w 2011 planet space sci 59 1559 1600 to help address this problem the global geological map provides a stratigraphic sequence of units and known areas where each unit is exposed on the planet for each crater on venus we identify the specific geological units predating and postdating the crater we perform a statistical analysis of this set of observations with a buffered crater density approach which rigorously and consistently takes into account the large size of craters and the fact that many craters are known to predate and or postdate more than one unit in this analysis we consider crater emplacement as random and resurfacing history as determined although unknown we obtain formal confidence intervals for the mean ages of geological units and the mean age differences between the pairs of units at the unit boundaries we find that 1 size frequency distributions of craters superposed on each unit are consistent with each other 2 regional plains and stratigraphically older units have similar crater retention ages 3 stratigraphically younger units have a mean crater retention age significantly younger than the regional plains these findings are readily and consistently explained by global resurfacing scenarios and are difficult to reconcile with equilibrium resurfacing scenarios our analysis also shows that the latest recorded part of intensive resurfacing period lasted on the order of 10 of the mean surface age tens of millions of years the termination of intensive resurfacing may or may not be synchronous over the planet our results also indicate that there are extended deposits associated with large craters that are almost indiscernible in the radar images but obscure radar contrasts between predating lava flows we do not see evidence for any significant and prolonged change of atmospheric pressure following the termination of the intensive resurfacing epoch

lineated valley fill and lobate debris apron stratigraphy in nilosyrtis mensae mars evidence for phases of glacial modification of the dichotomy boundary 1 the nilosyrtis mensae region is important among dichotomy boundary fretted terrain outcrops as it provides evidence of overprinting of ancient landscapes by a suite of glacial features providing a composite view of the variety of midlatitude glacial modification processes that can occur during recent martian ice ages on the basis of a series of criteria developed for the identification of a glacial origin for lineated valley fill and lobate debris aprons we interpret stratigraphic topographic and textural relationships between lineated valley fill and lobate debris apron morphological units as evidence of local and regional glacial overprinting of the landscape during the recent amazonian we document 1 stratigraphic relationships between lineated valley fill subunits including the presence of apparently superposed and small scale lobate features 2 the regional integration and flow of lineated valley fill material 3 lineated valley fill degradation and 4 the nature and stratigraphic position of lobate debris aprons these observations suggest multiple phases or episodes of midlatitude valley glacier activity these observations together with those of surface units elsewhere in northern arabia terra interpreted as glacially modified landforms suggest the possibility of midlatitude glacial deposits extending over broad portions of the martian dichotomy boundary within the past several hundred million years

permian wolfcamp limestone reservoirs powell ranch field eastern midland basin deep water carbonate channel reservoirs form important oil reservoirs along the toe of the eastern shelf of the permian basin in west texas in northwestern glasscock county these wolfcamp reservoirs are leonardian early permian in age and define high energy channels incised into surrounding carbonate detritus and basinal shale porous grain flow material filling these channels along with encasing detritus was derived from the shallow shelf located six miles to the east reservoirs are in packstone and grainstone facies and have significant interparticle and moldic porosity relevant exploration began in the 1960s but expanded slowly thereafter due to lack of success caused by complex patterns of channel occurrence results of a three dimensional 3 d seismic survey conducted in 1990 have greatly enhanced the identification and mapping of productive channels in the powell ranch field complex wells in this complex are capable of flowing 400 1200 bbl of oil per day and have reserves ranging from 0 2 to 1 3 mbo the new 3 d data have improved the relevant geologic model and dramatically increased rates of drilling success application of such data to this setting offers a potential model for other parts of the permian basin

amazonian aged fluvial valley systems in a climatic microenvironment on mars melting of ice deposits on the interior of lyot crater valley networks regional drainage patterns suggesting liquid water stability at the surface are confined to early in the history of mars the noachian hesperian boundary and before prior to a major climate transition to the hyperarid cold conditions of the amazonian several later fluvial valley systems have been documented in specific hesperian and early amazonian environments and are thought to have formed due to local conditions here we describe fluvial valley systems within lyot crater that have the youngest well constrained age reported to date middle or late amazonian for systems of this size tens of km these valleys are linked to melting of near surface ice rich units extend up to 50 km in length follow topographic gradients and deposit fans the interior of lyot crater is an optimal micro environment since its low elevation leads to high surface pressure and temperature conditions at its location in the northern mid latitudes are sufficient for melting during periods of high obliquity this micro environment in lyot apparently allowed melting of surface ice and the formation of the youngest fluvial valley systems of this scale yet observed on mars

late amazonian glaciation at the dichotomy boundary on mars evidence for glacial thickness maxima and multiple glacial phases lineated valley fill lvf in fretted valleys at the dichotomy boundary has been interpreted as glacial in origin unknown are 1 the original thickness of the glacier ice 2 the amount of ice surface lowering through sublimation and retreat to its presently observed level and 3 whether there were multiple periods of glaciation we address these questions through analysis of an lvf glacial system the elevation difference between the upper limit of a previous highstand and the current surface of the lvf at the study site is 920 m we interpret this difference to be the minimum amount of ice surface lowering of the glacier system consistent with a general lowering of the ice surface are multiple moraines and or trimlines and changes in lvf flow patterns as the ice retreated and decreased in thickness the superposition of several lobes onto the current surface of the lvf indicates that a phase of alpine glaciation followed the lowering of the valley glacial system these data suggest that the late amazonian glaciation that produced lvf in this region involved significantly larger amounts of ice than previously thought and that subsequent alpine glaciation followed

flow patterns of lobate debris aprons and lineated valley fill north of ismeniae fossae mars evidence for extensive mid latitude glaciation in the late amazonian a variety of late amazonian landforms on mars have been attributed to the dynamics of ice related processes evidence for large scale mid latitude glacial episodes existing within the last 100 million to 1 billion years on mars has been presented from analyses of lobate debris aprons lda and lineated valley fill lvf in the northern and southern mid latitudes we test the glacial hypothesis for lda and lvf along the dichotomy boundary in the northern mid latitudes by examining the morphological characteristics of lda and lvf surrounding two large plateaus proximal massifs and the dichotomy boundary escarpment north of ismeniae fossae centered at 45 3n and 39 2e lineations and flow directions within lda and lvf were mapped using images from the context ctx camera the thermal emission imaging spectrometer themis and the high resolution stereo camera hrsc flow directions were then compared to topographic contours derived from the mars orbiter laser altimeter mola to determine the down gradient components of lda and lvf flow observations indicate that flow patterns emerge from numerous alcoves within the plateau walls are integrated over distances of up to tens of kilometers and have down gradient flow directions smaller lobes confined within alcoves and superposed on the main lda and lvf represent a later less extensive glacial phase crater size frequency distributions of lda and lvf suggest a minimum youngest age of 100 ma the presence of ring mold crater morphologies is suggestive that lda and lvf are formed of near surface ice rich bodies from these observations we interpret lda and lvf within our study region to result from formerly active debris covered glacial flow consistent with similar observations in the northern mid latitudes of mars glacial flow was likely initiated from the accumulation and compaction of snow and ice on plateaus and in alcoves within the plateau walls as volatiles were mobilized to the mid latitudes during higher obliquity excursions together with similar analyses elsewhere along the dichotomy boundary these observations suggest that multiple glacial episodes occurred in the late amazonian and that lda and lvf represent significant reservoirs of non polar ice sequestered below a surface lag for hundreds of millions of years

a recent ice age on mars evidence for climate oscillations from regional layering in mid latitude mantling deposits 1 two end member hypotheses have been proposed to account for the emplacement and distribution of ice in the near subsurface of mars at mid to high latitudes during recent spin axis orbital variation induced climate change in the first diffusion of atmospheric water vapor into and out of a porous regolith forms ice cemented soils whose latitudinal stability migrates as a function of orbitally controlled climatic conditions in the alternative hypothesis atmospheric deposition of ice snow and dust produces dusty ice rich layers during periods of higher obliquity new image data reveal meters thick layered deposits exposed on mid latitude pole facing slopes supporting the latter hypothesis these observations suggest that the near surface ice detected by the grs instrument suite and the phoenix lander at high latitudes is linked to thick buried ice that was atmospherically deposited during recent ice ages and that significant amounts of subsurface ice may remain today in the 30 50 mid latitude regions where fresh craters imaged by hirise expose abundant ice

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

extensive middle amazonian mantling of debris aprons and plains in deuteronilus mensae mars implications for the record of mid latitude glaciation abstract the mid latitudes of mars are host to a record of recent episodes of accumulations of ice rich materials the record includes debris aprons interpreted to be debris covered glaciers that may represent the preserved remnants of a much more extensive ice sheet we assessed the possibility of former glacial extents by examining debris aprons and the surrounding plains in deuteronilus mensae geomorphic units and stratigraphic relationships were mapped and documented from mars reconnaissance orbiter mro context ctx and high resolution imaging science experiment hirise camera images and crater retention ages were estimated from crater size frequency distributions three major units are observed within the study area debris aprons lower plains and upper plains debris aprons exhibit characteristics typical for these features documented elsewhere and in previous studies including integrated flow lineations and patterns convex upward profiles and knobby and brain terrain surface textures a lower bound on the age for debris aprons is estimated to be 0 9 ga debris aprons are superposed on a lower plains unit having a lower bound age of 3 3 3 5 ga a 50 100 m thick upper plains unit superposes both debris apron landforms and lower plains units and has a best fit minimum age of 0 6 ga the upper plains unit exhibits characteristics of atmospherically emplaced mantle material including fine grained nature sublimation textures cyclic layering draping character and widespread spatial distribution fracturing and subsequent sublimation erosion of upper plains on debris aprons has contributed to many of the surface textures on debris aprons the upper plains unit has also been eroded from the lower plains and plateaus evidenced by isolated blocks of upper plains in the interiors of craters and on the walls and tops of plateaus while no conclusive evidence diagnostic of former cold based ice sheets are observed in the plains within the study region such landforms and units may have been poorly developed or absent as is often the case on earth and would have been covered and reworked by later mantling episodes these observations suggest that emplacement of thick ice rich mantle deposits extended at least to near the early middle amazonian boundary and overlapped with the waning stages of glaciation in deuteronilus mensae

redefinition of the crater density and absolute age boundaries for the chronostratigraphic system of mars abstract for the boundaries of each chronostratigraphic epoch on mars we present systematically derived crater size frequencies based on crater counts of geologic referent surfaces and three proposed standard crater size frequency production distributions as defined by a a simple 2 power law b neukum and ivanov c hartmann in turn these crater count values are converted to model absolute ages based on the inferred cratering rate histories we present a new boundary definition for the late hesperian early amazonian transition our fitting of crater size frequency distributions to the chronostratigraphic record of mars permits the assignment of cumulative counts of craters down to 100 m 1 km 2 km 5 km and 16 km diameters to martian epochs due to differences in the standard crater size frequency production distributions a generalized crater density based definition to the chronostratigraphic system cannot be provided for the diameter range used for the boundary definitions the resulting model absolute age fits vary within 1 5 for a given set of production function and chronology model ages crater distributions translated to absolute ages utilizing different curve descriptions can result in absolute age differences exceeding 10

tephra deposition on glaciers and ice sheets on mars influence on ice survival debris content and flow behavior we examine the consequences of pyroclastic deposits being emplaced onto ice layers on mars both those in the polar caps and those forming glaciers on the flanks of some of the large shield volcanoes we show that layers of pyroclasts greater than a few meters in thickness whether emplaced cold as fall deposits or hot as pyroclastic density current deposits act almost exclusively to protect ice layers beneath them from sublimation irrespective of whether they are emplaced at high or low elevations or high or low latitudes layers less than about 2 m thick on the other hand can cause significant ice loss by raising the surface temperature due to their low albedo and then transmitting that increased temperature to the underlying ice especially on a diurnal time scale this can have a significant bearing on the emplacement history of polar water ice and on the survival time of glacial ice on shield volcano flanks a key factor in the latter case is the timing of the episodic volcanic activity relative to the cycles of climate change driven by mars obliquity and eccentricity variations

topography of mars from global mapping by hrsc high resolution digital terrain models and orthoimages characteristics and performance abstract we report on the results of the mars express high resolution stereo camera hrsc experiment pertaining to one of its major aims mapping the surface of mars by high resolution digital terrain models dtm up to 50 m grid spacing and orthoimages up to 12 5 m resolution we introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation we also address the performance characteristics of the mapping project related to different aspects of internal accuracy accuracy with respect to the global reference system and regional aspects using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data a mean precision of the resulting 3d points of about 12 m is obtained exceeding the mean ground resolution of the stereo images using mars orbiter laser altimeter mola data the hrsc models are firmly tied to the global reference system at the scale of the hrsc dtm grid spacing in the lateral dimension and to within few meters vertically hrsc high resolution dtms are typically generated using a grid size of about 2 times the mean ground resolution but usually not larger than 3 times the mean ground resolution and not smaller than 3 times the precision of the integrated 3d points derived from stereo image analysis statistically every grid cell is based on at least one measured 3d point thus horizontal dtm resolution is well established with regard to the precision and density of the derived 3d points while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued comparison with the dtm derived from mola data allows us to identify specific advancements related to this updated view of martian topography we also address the mapping performance of hrsc in comparison to mola with respect to latitude and to different surface types and morphologies finally comparison with mola highlights typical complementarities of the two different approaches for mapping planetary surfaces

cold based debris covered glaciers evaluating their potential as climate archives through studies of ground penetrating radar and surface morphology we describe the morphology and internal structure of mullins and friedman glaciers two cold based debris covered alpine glaciers that occur in neighboring valleys in the mcmurdo dry valleys antarctica both glaciers are overlain by a single dry supraglacial debris layer 8 75 cm thick each mantling debris layer is marked with near identical patterns of arcuate ridges and steps as well as corresponding changes in bulk grain size meter scale surface topography and thermal contraction crack polygons results from 24 km of ground penetrating radar data show that the ice within the uppermost 1 2 km of mullins and friedman glaciers is essentially free of englacial debris 1 by volume but thereafter is interspersed with bands of englacial debris each 3 m thick and dipping up glacier that intersect the ice surface at all major surface ridges and steps the similarity in number and pattern of englacial debris bands and corresponding surface ridges and steps across both glaciers along with model results and observations that call for negligible basal entrainment is best explained by episodic environmental change at valley headwalls our working hypothesis is that layers of englacial debris originate as supraglacial lags that form in ice accumulation areas during times of reduced net ice accumulation following renewed net ice accumulation these lags are subsequently buried by snow and ice flow englacially and intersect the ice surface to impart distinctive changes in the texture of supraglacial debris and topographic relief the implication is that the englacial structure and surface morphology of these cold based debris covered glaciers preserves a consistent record of climate and environmental change

fault zone structure from topography signatures of en echelon fault slip at mustang ridge on the san andreas fault monterey county california 1 we used high resolution topography to quantify the spatial distribution of scarps linear valleys topographic sinks and oversteepened stream channels formed along an extensional step over on the san andreas fault saf at mustang ridge california this location provides detail of both creeping fault landform development and complex fault zone kinematics here the saf creeps 10 14 mm yr slower than at locations 20 km along the fault in either direction this spatial change in creep rate is coincident with a series of en echelon oblique normal faults that strike obliquely to the saf and may accommodate the missing deformation this study presents a suite of analyses that are helpful for proper mapping of faults in locations where high resolution topographic data are available furthermore our analyses indicate that two large subsidiary faults near the center of the step over zone appear to carry significant distributed deformation based on their large apparent vertical offsets the presence of associated sag ponds and fluvial knickpoints and the observation that they are rotating a segment of the main saf several subsidiary faults in the southeastern portion of mustang ridge are likely less active they have few associated sag ponds and have older scarp morphologic ages and subdued channel knickpoints several faults in the northwestern part of mustang ridge though relatively small are likely also actively accommodating active fault slip based on their young morphologic ages and the presence of associated sag ponds

radar evidence for ice in lobate debris aprons in the mid northern latitudes of mars 1 subsurface radar sounding data indicate that lobate debris aprons found in deuteronilus mensae in the mid northern latitudes of mars are composed predominantly of water ice the position in time delay and the relatively low amount of signal loss of the apparent basal reflectors below the debris aprons indicate that aprons contain only a minor component of lithic material the current presence of large ice masses at these latitudes has important implications for the climate evolution of mars and for future targets for in situ exploration

northern mid latitude glaciation in the late amazonian period of mars criteria for the recognition of debris covered glacier and valley glacier landsystem deposits lobate debris aprons lda and lineated valley fill lvf have been known to characterize the mid latitude regions of mars since documented by viking their flow like character suggested that deposition of ice in talus pile pore space caused lubrication and flow during an earlier climatic regime a number of factors have remained uncertain however including the detailed structure and texture of lda lvf the relationships between them their direction of flow the origin and abundance of the lubricating agent and their exact mode of origin e g ice assisted rock creep ice rich landslides rock glaciers debris covered glaciers we use new high resolution stereo camera hrsc image and topography data in conjunction with a range of other post viking data sets and new insights provided by cold based terrestrial glacial analogs to assess the characteristics of lda lvf in the northern mid latitudes of mars we find evidence that the characteristics and flow patterns of the lda and lvf are most consistent with late amazonian debris covered glacial valley landsystems the broad distribution and integrated characteristics of the lda lvf systems suggest that earlier in the amazonian climatic conditions were such that significant snow and ice accumulated on mid latitude plateaus and in valleys producing integrated glacial landsystems the remnants of which are preserved today beneath residual sublimation till derived from adjacent valley walls atmospheric general circulation models suggest that these climatic conditions occurred when mars was at a spin axis obliquity of 35 and the atmosphere was relatively dusty glacial flow modeling under these conditions produces patterns similar to those documented in the lda lvf and sharad radar data suggests that significant amounts of ice remain sequestered below the sublimation lag today

lineated valley fill at the martian dichotomy boundary nature and history of degradation the fretted terrain of the martian dichotomy boundary is a key region for investigating landforms related to creep of ice and debris as it exhibits landforms comparable to morphologies of periglacial environments although features known as lobate debris aprons lineated valley fills and concentric crater fills have been studied in great detail basic questions concerned with the composition and the style of emplacement and degradation still remain unanswered this study focuses on morphologies which are located in a neara circular depression located at the dichotomy escarpment in deuteronilus mensae analysis of higha resolution image data suggests an early formation of these features as the result of backward thermokarstic degradation of highland terrain geologically younger processes caused deposition and degradation of an icea rich mantling deposit which ultimately led to formation of creep morphologies that might have even been active in the geologically recent past intermixing of both degradational landform units form complex patterns that cannot be explained by a late stage glacial process alone morphological comparisons of lineated valley fill units with concentric crater fill landforms in utopia planitia strongly suggest comparable emplacement and degradation styles of these features the sequential development consisting of an initial probably widespread thermokarstic degradation followed by later cyclic deposition of volatile material and continual thermokarstic degradation suggests that the development of parts of the martian fretted terrain is directly related to climatic variations in the planeta s history

an atmospheric blast thermal model for the formation of high latitude pedestal craters although tenuous the atmosphere of mars affects the evolution of impact generated vapor early time vapor from a vertical impact expands symmetrically directly transferring a small percentage of the initial kinetic energy of impact to the atmosphere this energy in turn induces a hemispherical shock wave that propagates outward as an intense airblast due to high speed expansion of vapor followed by a thermal pulse of extreme atmospheric temperatures from thermal energy of expansion this study models the atmospheric response to such early time energy coupling using the cth hydrocode written at sandia national laboratories results show that the surface surrounding a 10 km diameter crater 6 km apparent diameter on mars will be subjected to intense winds 200 m s and extreme atmospheric temperatures these elevated temperatures are sufficient to melt subsurface volatiles at a depth of several centimeters for an ice rich substrate ensuing surface signatures extend to distal locations 4 apparent crater diameters for a case of 0 1 energy coupling and include striations thermally armored surfaces and or ejecta pedestals all of which are exhibited surrounding the freshest high latitude craters on mars the combined effects of the atmospheric blast and thermal pulse resulting in the generation of a crater centered erosion resistant armored surface thus provide a new very plausible formation model for high latitude martian pedestal craters

formation of lobate debris aprons on mars assessment of regional ice sheet collapse and debris cover armoring abstract lobate debris aprons lda are lobate shaped aprons surrounding scarps and isolated massifs that are concentrated in the vicinity of the northern dichotomy boundary on mars ldas have been interpreted as 1 ice cemented talus aprons undergoing viscous flow 2 local debris covered alpine like glaciers or 3 remnants of the collapse of a regional retreating ice sheet we investigate the plausibility that ldas are remnants of a more extensive regional ice sheet by modeling this process we find that as a regional ice sheet collapses the surface drops below cliff and massif bedrock margins exposing bedrock and regolith and initiating debris deposition on the surface of a cold based glacier reduced sublimation due to debris cover armoring of the proto lda surface produces a surface slope and consequent ice flow that carries the armoring debris away from the rock outcrops as collapse and ice retreat continue the debris train eventually reaches the substrate surface at the front of the glacier leaving the entire lda armored by debris cover using a simplified ice flow model we are able to characterize the temperature and sublimation rate that would be necessary to produce ldas with a wide range of specified lateral extents and thicknesses we then apply this method to a database of documented lda parameters height lateral extent from the dichotomy boundary region and assess the implications for predicted climate conditions during their formation and the range of formation times implied by the model we find that for the population examined here typical temperatures are in the range of 85 to 40 c and typical sublimation rates lie in the range of 6 14 mm a lobate debris apron formation times from the point of bedrock exposure to complete debris cover cluster near 400 500 ka these results show that lda length and thickness characteristics are consistent with climate conditions and a formation scenario typical of the collapse of a regional retreating ice sheet and exposure of bedrock cliffs this scenario helps resolve many of the unusual characteristics of lobate debris aprons lda and lineated valley fill lvf for example the distribution of lvf is very consistent with extensive flow of glacial ice from plateau icefields and the acquisition of a debris cover in the waning stages of retreat of the regional cover as the bedrock scarps are exposed the typical concentric development of lda around massifs is much more consistent with ice sheet retreat than insolation related local accumulation and flow we thus conclude that the retreating ice sheet model is robust and should be investigated and tested in more detail in addition these results clearly show that the lobate debris aprons in the vicinity of the dichotomy boundary could not have attained temperatures near or above the ice melting point and retained their current shape a finding that supports subzero temperatures for the last several hundred million years the age of the lda surfaces a further implication is that the lda ice has been preserved for at least several hundred million years and could potentially contain the record of the climate of mars preserved since that time below a sublimation lag deposit

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

latitude dependence of martian pedestal craters evidence for a sublimation driven formation mechanism we report on the results of a survey to document and characterize pedestal craters on mars equatorward of similar to 60 degrees n and 65 degrees s latitude the identification of 2696 pedestal craters reveals a strong latitude dependence with the vast majority found poleward of 33 degrees n and 40 degrees s this latitudinal extent is correlated with many climate indicators consistent with the presence of an ice rich substrate and with climate model predictions of where ice is deposited during periods of higher obliquity in the amazonian we have measured key physical attributes of pedestal craters including the farthest radial extents of the pedestals pedestal heights and the circularity of the pedestal margins in conjunction with the geographic distribution our measurements strongly support a sublimation related formation mechanism this is in contrast to previous hypotheses which have relied on eolian deflation to produce the elevated plateaus the identification of marginal pits on the scarps of some pedestal craters interpreted to be sublimation pits provide direct evidence for the presence of ice rich material underlying the armored surface of pedestal craters on the basis of our findings we propose a formation mechanism whereby projectiles impact into a volatile rich dust snow ice substrate tens to hundreds of meters thick overlying a dominantly fragmental silicate regolith the area surrounding the resulting crater becomes armored pedestals extend to a distance of multiple crater radii farther than typical ejecta deposits necessitating an armoring mechanism that is capable of indurating the surface to a distance greater than the reach of the ejecta return to low obliquity causes sublimation of the volatile rich layer from the intercrater plains lowering the elevation of the regional terrain this yields generally circular pedestal craters elevated above the surrounding plains as a result the armored surfaces of pedestal craters have preserved a significant record of amazonian climate history in the form of ice rich deposits

amazonian northern mid latitude glaciation on mars a proposed climate scenario recent geological observations in the northern mid latitudes of mars show evidence for past glacial activity during the late amazonian similar to the integrated glacial landsystems in the dry valleys of antarctica the large accumulation of ice many hundreds of meters required to create the observed glacial deposits points to significant atmospheric precipitation snow and ice accumulation and glacial flow in order to understand the climate scenario required for these conditions we used the lmd laboratoire de meteorologie dynamique mars gcm general circulation model which is able to reproduce the present day water cycle and to predict past deposition of ice consistent with geological observations in many cases prior to this analysis however significant mid latitude glaciation had not been simulated by the model run under a range of parameters in this analysis we studied the response of the gcm to a wider range of orbital configurations and water ice reservoirs and show that during periods of moderate obliquity 25 35 and high dust opacity sdust 1 5 2 5 broad scale glaciation in the northern mid latitudes occurs if water ice deposited on the flanks of the tharsis volcanoes at higher obliquity is available for sublimation we find that high dust contents of the atmosphere increase its water vapor holding capacity thereby moving the saturation region to the northern mid latitudes precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems producing surface ice distribution and amounts that are consistent with the geological record ice accumulation rates of 10 mm yr

vaduz an unusual fresh crater on mars evidence for impact into a recent ice rich mantle 1 a fresh 1 85 km diameter impact crater in the midlatitudes of mars 38 n named vaduz exhibits distinctive crater related geological subunits facies extending up to 15 radii from the rim crest and perched 10 m above the adjacent plains knobby terrain fringing and underlying the facies is interpreted as degraded thermal contraction crack polygons consistent with an ice rich mantle buried by ejecta the almost complete regional disappearance of this ice rich unit and consequent lowering of regional topography by over ten meters is interpreted to mean that the ice rich mantle was formed by climate related deposition of snow ice and dust during recent periods of high obliquity transition to lower obliquity and the attendant poleward retreat of the mantling unit is the most likely cause of the regional loss of the ice rich layer the depth of this crater relative to the thickness of the ice rich unit indicates that the impact event excavated bedrock and that vaduz can be classified as an excess ejecta crater excavated silicate regolith and fragmented target debris appear to have been an important factor in the armoring mechanism citation schaefer e i j w head and s j kadish 2011 vaduz an unusual fresh crater onmars evidenceforimpactintoarecentice richmantle geophys

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

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

volume of martian midlatitude glaciers from radar observations and ice flow modeling numerous glacier like forms have been identified in the midlatitudes of mars and within recent years the acquisition of radar sounding data has revealed that the features are chiefly composed of water ice here we use radar observations in combination with ice flow models and inverse methods to calculate the volume of ice present at the midlatitudes of mars in order to obtain ice thicknesses we infer the yield stress of the ice deposits and we find that they are consistently lower than those of most terrestrial glaciers we estimate the present ice volume of lobate debris aprons identified by levy et al 2014 on mars to correspond to 1 55 105 km3 with an uncertainty of 25 this corresponds to a global ice cover of 1 1m thus the water ice found at midlatitudes is an important water reservoir and an important part of the global surface ice budget

sinton crater mars evidence for impact into a plateau icefield and melting to produce valley networks at the hesperian amazonian boundary abstract the majority of martian valley networks are found on noachian aged terrain and are attributed to be the result of a warm and wet climate that prevailed early in mars history younger valleys have been identified though these are largely interpreted to be the result of localized conditions associated with the melting of ice from endogenic heat sources sinton crater a 60 km diameter impact basin in the deuteronilus mensae region of the dichotomy boundary is characterized by small anastomosing valley networks that are located radial to the crater rim large scale deposits interpreted to be the remains of debris covered glaciers have been identified in the area surrounding sinton and our observations have revealed the occurrence of an ice rich fill deposit within the crater itself we have conducted a detailed investigated into the sinton valley networks with all the available remote data sets and have dated their formation to the amazonian hesperian boundary the spatial and temporal association between sinton crater and the valley networks suggest that the impact was responsible for their formation we find that the energy provided by an asteroid impact into surficial deposits of snow ice is sufficient to generate the required volumes of melt water needed for the valley formation we therefore interpret these valleys to represent a distinct class of martian valley networks this example demonstrates the potential for impacts to cause the onset of fluvial erosion on mars our results also suggest that periods of glacial activity occurred throughout the amazonian and into the hesperian in association with variations in spin orbital parameters

quantification of waste morphology in martian fretted terrain extensive geomorphic mapping in the northern martian fretted terrain of deuteronilus and protonilus mensae shows details of the wastedominated landform association in this region wasting appears to have occurred along the cratered terrain boundary ctb at the expense of old cratered terrain north of the boundary remnants of old cratered terrain occur as island mesas surrounded by extensive debris aprons quantitative study using principal components analysis pca reveals distinct spatial variations in the morphology of waste forms in the egion and supports the qualitative interpretations made during geomorphic mapping these organized spatial patterns occur with respect to longitude and latitude and therefore with reference to distance from the ctb and provide clues to the degradational history of the region analyses of the individual landforms irrespective of their location to the ctb indicate strong structural control of their form mesas appear to evolve from equant forms to narrow ridges with large debris aprons after they become detached from the old cratered terrain the success of pca in explaining patterns in degradational landforms suggests that pca may be an important technique in quantifying the geomorphic evolution of the martian surface

deposition and degradation of a volatile rich layer in utopia planitia and implications for climate history on mars 1 we investigate the surface morphology of a study area in western utopia planitia mars which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes polygonally fractured ground and thermokarst like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters we observe a latitudinal dependence of the degradation of this mantling deposit larger depressions whose floors reveal the underlying basement rocks cover a higher fraction of the total terrain in the southern part of the study area than in the northern part indicating a more intense degradation of the mantle in the south all depressions have an asymmetric cross section in north south direction interpreted to be the result of the different solar radiation on differently oriented slopes on the basis of our morphological observations we develop a conceptual model for landscape evolution in western utopia planitia it involves subaerial deposition of a layered ice rich mantle and its subsequent degradation by polygon formation and sublimation a terrestrial analog to the polygonally fractured mantling deposit and its thermokarst like depressions is the siberian ice complex or yedoma which consists of subaerial ice rich deposits and is connected to nonglaciated landscapes with highly continental cold climatic environmental conditions our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western utopia however the young age of the deposition and degradation implies climatic excursions in the very recent past on mars