planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

tectonic geomorphology of the southeastern mississippi embayment in northern mississippi usa we analyzed drainage basin geometry in part of the southeastern mississippi embayment near the new madrid seismic zone in order to detect areas of lateral stream migration that could indicate recent tectonism toward this goal a field of drainage basin asymmetry vectors was generated from a digital terrain model and compared to geologic structure lithofacies seismicity remotely sensed lineaments and major drainage divides transverse topographical drainage basin asymmetry t index results define geomorphic domains in northern mississippi 33 to 35 n 88 5 to 90 25 w that may reflect deep crustal blocks bounded by active faults or flexures t index measurements a proxy for lateral stream migration of more than 4500 second order drainage basins produced a two dimensional field of 282 spatially averaged vectors from which we interpreted 12 domains some domain boundaries correspond to mapped faults of two paleozoic fault systems in our study area the northeast striking mississippi valley graben system and the northwest striking ouachita thrust belt and foreland faults several other prominent domain boundaries may be previously unmapped faults flexures parallel to these systems this interpretation is supported by satellite image analysis of the northeastern study area which reveals lineaments consistent with our domain boundaries that have strikes that reflect the regional subsurface structural grain

a hydrological continuum in permafrost environments the morphological signatures of melt driven hydrology on earth and mars abstract this paper examines relationships between the morphology of cold desert hydrological features and the water sources and it relates the formation of diagnostic deposits and erosion patterns to environmentally controlled patterns of discharge in particular three sets of landforms found in the mcmurdo dry valleys of antarctica are compared to similar features on mars antarctic streams rivers to amazonian valleys terrestrial gullies to martian gullies and water tracks to recurring slope lineae similarities in landform morphology are highlighted for each set hydrological characteristics are aggregated or calculated and they are shown to scale comparably across the landforms for the terrestrial and martian groups accordingly a hydrological continuum is proposed linking the magnitude and the persistence of water sources in cold desert environments to flow response and the formation of diagnostic landforms this concept provides a framework for examining the relationships between climate hydrology and geomorphology in the cold desert environments of these two worlds

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

mineral abundances at the final four curiosity study sites and implications for their formation abstract a component of the landing site selection process for the mars science laboratory msl involved the presence of phyllosilicates as the main astrobiological targets gale crater was selected as the msl landing site from among 4 down selected study sites gale eberswalde and holden craters mawrth vallis that addressed the primary scientific goal of assessing the past habitability of mars a key constraint on the formation process of these phyllosilicate bearing deposits is in the precise mineralogical composition we present a reassessment of the mineralogy of the sites combined with a determination of the modal mineralogy of the major phyllosilicate bearing deposits of the four final study sites from the modeling of near infrared spectra using a radiative transfer model the largest abundance of phyllosilicates 30 70 is found in mawrth vallis the lowest one in eberswalde http www nasa gov mission pages msl news msl20130312 html is consistent with the compositions modeled for the eberswalde and holden deltaic rocks at gale the paucity the small diversity and the low abundance of nontronite do not favor a complex and long drainage system localized aqueous processes in space and time environments could have produced both nontronites and sulfates however most materials in gale are unfortunately dust covered so that orbital data are limited by spatial resolution and surficial fines that could dilute and obscure the spectral influence of phyllosilicates in the rocks potential formation processes of diverse and abundant mawrth vallis deposits include low temperature hydrothermal alteration in marine environments and or pedogenesis

determining the three dimensional geometry of a dike swarm and its impact on later rift geometry using seismic reflection data dike swarm emplacement accommodates extension during rifting and large igneous province lip formation with ancient dike swarms serving to localize strain during later tectonic events deciphering three dimensional 3 d dike swarm geometry is critical to accurately calculating magma volumes and magma assisted crustal extension allowing syn emplacement mantle and tectonic processes to be interrogated it is also important for quantifying the influence of ancient dike swarms on post emplacement faulting however the essentially 2 d nature of earth s surface combined with the difficulties in imaging subvertical dikes in seismic reflection data and the relatively low resolution of geophysical data in areas of active diking means our understanding of dike swarm geometry at depth is limited we examine an 25 km wide 100 km long west southwest trending dike swarm imaged due to post emplacement rotation to shallower dips in high quality 2 d and 3 d seismic reflection data offshore southern norway tuned reflection packages correspond to thin 75 m thick closely spaced dikes these data provide a unique opportunity to image and map an ancient dike swarm at variable structural levels crosscutting relationships indicate emplacement occurred in the late carboniferous early permian and was linked to the formation of the ca 300 ma skagerrak centered lip dike swarm width increases with depth suggesting that magma volume and crustal extension calculations based on surface exposures are dependent on the level of erosion during the mesozoic rift related faults localized above and exploited mechanical anisotropies within the dike swarm we demonstrate that seismic reflection data are a powerful tool in understanding dike swarm geometry and the control of dikes on subsequent faulting

weak bedrock allows north south elongation of channels in semi arid landscapes abstract differences in the lengths of pole and equator facing slopes are observed in a variety of landscapes these differences are generally attributed to relative variations in the intensity of mass transport processes on slopes receiving different magnitudes of solar radiation by measuring anomalies in the planform characteristics of drainage networks we demonstrate that in the most asymmetric landscapes this asymmetry primarily arises from the equator ward alignment of low order valley networks valley network asymmetry is more severe in rocks expected to offer little resistance to erosion than in more resistant rocks when controlling for climate this suggests that aspect driven differences in surface processes that drive differences in landscape evolution are also sensitive to underlying rock type

comprehensive analysis of glaciated martian crater greg abstract the 66 km diameter martian crater greg east of hellas hosts various distinctive features including dendritic valleys filled with chevron textured masses south wall and lobate tongues a few kilometers long north wall we analyze these features by various quantitative techniques to illuminate martian geologic and climatic history crater retention model ages indicate that greg is at least 1 3 gy old but surface layers of mantles and glacial features are orders of magnitude younger properties of the dendritic valleys combined with climate models suggest that fluvial activity began under a thicker warmer atmosphere soon after the crater s formation the oldest exposed fluvial systems have surface crater retention ages of a few hundred my indicating runoff in recent geologic time much of greg is covered by ice rich mantle deposits for which we infer gradual accumulation and depths of order 30 85 m they mask pre existing landforms the lobate tongues are interpreted as glaciers with mean slope of 10 2 2 3 and average thickness of 33 19 m our calculations and data suggest that these glaciers were originally ice rich and that their surface layers have been depleted by volatile loss the glaciers probably formed when ice rich mantle deposits reached critical thickness and flowed downhill the top 5 10 m of the mantle and glaciers show crater survival times of order a few my to 15 my which remarkably is the time since the last 1 4 episodes of obliquity 45 global climate models affirm that greg lies in one of two non polar areas with extremes of ice deposition during high obliquity epochs this match with observations supports the use of such models in studies of planetary climate change

the geology and mineralogy of ritchey crater mars evidence for post noachian clay formation widespread detection of phyllosilicates clay minerals in noachian 3 5 ga terrains on mars and their paucity in younger terrains have led to the hypothesis that noachian conditions were more clement than the colder drier conditions that have since followed however recent clay detections in several hesperian impact craters suggest that fluvial transport and alteration were possible after the posited early era of phyllosilicate formation here we present evidence that rocks within hesperian age ritchey crater 28 5 s 51 w record a period of post noachian fluvial transport and in situ alteration this resulted in the transport of clays from the crater wall to the crater floor and the formation of hydrated silica and fe mg smectite in ritchey s central uplift clay minerals associated with central uplifts are commonly interpreted to represent preexisting clays excavated from depth potentially providing insight into older crustal clay forming processes here we present detailed geomorphic and mineralogic maps and show that the clays in ritchey s central peak formed after or as a direct result of the impact and are thus hesperian or younger clays on the crater wall were either preexisting clays exposed by the impact or formed in situ through postimpact water rock interaction in either scenario some of these clays were likely subsequently transported to the crater floor by fluvial alluvial processes in a source to sink system in this context the hydrated phases in ritchey indicate several different formation and transport mechanisms and provide further evidence that near surface clay mineral formation and thus habitable conditions existed on mars after the noachian

eco geomorphic implications of hillslope aspect inferences from analysis of landscape morphology in central new mexico 1 we investigate the influence of hillslope aspect on landscape morphology in central new mexico where differences in soils vegetation and landforms are observed between mesic north facing and xeric south facing slopes slope area and curvature area relations derived from a digital elevation model dem are used to characterize the opposing hillslope morphologies in all geologies and elevation ranges studied topographic data reveal significantly steeper slopes in north facing aspects and shallower slopes in south facing aspects north facing slope curvatures are also greater than south facing curvatures using a conceptual slope area model we suggest that for a given drainage area steeper north facing slopes imply lower soil erodibility we argue that this interpretation consistent with recent views of ecosystem control on semiarid erosion rates shows the influence hillslope aspect on topography and its associated vegetation communities observed valley asymmetry in the region reinforces this concept and suggests a long term legacy of aspect modulated ecogeomorphic processes

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

errors in martian paleodischarges skew interpretations of hydrologic history case study of the aeolis dorsa mars with insights from the quinn river nv abstract changes in martian fluvial geomorphology with time stratigraphic age including decreases in paleochannel widths suggest waning paleodischarges through time where fluvial landforms do not preserve paleochannel widths e g meander deposits other landform dimensions i e radius of curvature may be used to estimate paleodischarges in the aeolis dorsa region topographically inverted and stacked fluvial deposits wide meander point bars overlain by thin channel fills preserve ostensible evidence of decreasing paleodischarges through time however a robust paleohydraulic analysis of these distinct deposits requires knowledge of the accuracy of a terrestrial based empirical relationship that estimates channel width from point bar radius of curvature we assess the accuracy of this radius width relationship by applying it to a well studied terrestrial analog the quinn river nevada we find that radii of curvature from the quinn river exceed the values predicted from the empirical relationship these anomalously high radii are associated with greater resistance in the channel cut banks indicating that bank strength is a confounding factor in the radius width relationship some deposits in the aeolis dorsa include irregular meander morphologies suggesting variably resistant channel banks and overestimates of both paleochannel widths and paleodischarges furthermore the morphometry of the overlying thin channel fills suggests their widths have been eroded such that their paleodischarges are underestimates these overestimates and underestimates when considered together suggest little change in paleodischarge during the stratigraphic transition from meander deposits to channel fills this work demonstrates the importance of terrestrial analog studies for revealing confounding factors in martian fluvial systems and cautions against simplistic interpretations of martian fluvial history the discovered inaccuracies of paleodischarge estimates expose sources of uncertainty in the extant paleodischarge data that bias inferences toward waning hydrologic activity through time

quantitative assessment of uncertainties in modeled crater retention ages on mars abstract with increasing high resolution coverage of mars surface crater count analysis is being used to estimate the formative ages of small depositional features 3 ga than nearby fans 1 3 ga this analysis provides a simple quantitative framework for assigning probable surface age ranges for small features on mars

origin and development of theater headed valleys in the atacama desert northern chile morphological analogs to martian valley networks abstract understanding planetary landforms including the theater headed valleys box canyons of mars usually depends on interpreting geological processes from remote sensing data without ground based corroboration here we investigate the origin and development of two mars analog theater headed valleys in the hyperarid atacama desert of northern chile previous workers attributed these valleys to groundwater sapping based on remote imaging topography and publications on the local geology we evaluate groundwater sapping and alternative hypotheses using field observations of characteristic features strength measurements of strata exposed in headscarps and estimates of ephemeral flood discharges within the valleys the headscarps lack evidence of recent or active seepage weathering such as spring discharge salt weathering alcoves or vegetation their welded tuff caprocks have compressive strengths multiple times those of the underlying epiclastic strata flood discharge estimates of cubic meters to tens of cubic meters per second derived using the manning equation are consistent with the size of transported clasts and show that the ephemeral streams are geomorphically effective even in the modern hyperarid climate we interpret that headscarp retreat in the quebrada de quisma is due to ephemeral flood erosion of weak miocene epiclastic strata beneath a strong welded tuff with erosion of the tuff facilitated by vertical jointing the quebrada de humayani headscarp is interpreted as the scar of a giant landslide maintained against substantial later degradation by similar strong over weak stratigraphy this work suggests that theater headed valleys on earth and mars should not be attributed by default to groundwater sapping as other processes with lithologic and structural influences can form theater headscarps

relative size of fluvial and glaciated valleys in central idaho quantitative comparisons of the morphometry of glaciated and fluvial valleys in central idaho were used to investigate the differences in valley relief and width in otherwise similar geologic and geomorphic settings the local relief width and cross sectional area of valleys were measured using gis software to extract information from usgs digital elevation models hillslope gradients were also measured using gis software power law relationships for local valley relief width and cross sectional area as a function of drainage area were developed local valley relief in glaciated valleys relates to drainage area with a power law exponent similar to fluvial valleys but glaciated valleys are deeper for a given drainage area local valley width in glaciated valleys is greater than in fluvial valleys but the exponent of the power law relationship to drainage area is similar in both valley types local valley cross sectional area in glaciated valleys increases with drainage area with a power law exponent similar to fluvial valleys however glacial valleys have roughly 80 greater cross sectional area steep valley walls in glaciated basins increase the potential for bedrock landsliding relative to fluvial basins both the olympic mountains of washington and valleys in central idaho show relationships in which glaciated valleys are up to 30 deeper than fluvial valleys despite differences in lithology tectonic setting and climate

detailed mapping of shallow landslides in eastern oklahoma and western arkansas and potential triggering by oklahoma earthquakes abstract landslides have long been considered one of the main erosive drivers that sculpt hillslopes over time tectonic forces raise slopes that can be sculpted by climate and the degree to which they can be sculpted depends upon the underlying lithology and hillslope geomorphology landslides destroy life and property and contribute to the evolution of mountain landscapes by generating and transporting hillslope sediments in this study we investigate the dynamics of soil mantled hillslopes in eastern oklahoma and western arkansas usa by mapping shallow landslides evaluating the frequency and magnitude of the landslides and quantifying the surface geometries we mapped 185 shallow landslides in a 150 km2 area the approximate ages of landslides and the frequencies and magnitudes area volume and runout were estimated using historical aerial photographs the landslide database was then used to compute rate of landslide occurrence and sediment yield in addition landslide surface geometries including slope curvature and surface roughness were determined from 10 m ned and 2 m lidar elevation data the hillslope susceptibility studies derived from elevation data were augmented by our review of common historical accounts that link landslides in the study region to the 1952 m 5 4 el reno oklahoma earthquake 300 km away in light of that case study we determined the frequency of historical earthquakes that impart 2 kpa dynamic stresses for the study area since 1900 and find an increased potential for dynamic stress perturbation of landslide activity since 2010 all these characteristics were then evaluated to understand the dynamics of hillslopes and hillslope susceptibility to shallow landslides frequency assessment of mapped landslides suggested that frequency of landslides increased significantly during 2005 2016 compared to 1995 2005 on average 10 shallow landslides occurred every year during 2005 2016 these landslides alone contributed 1 5 105 m3 yr sediment yield rate 0 10 cm yr of sediments surface roughness values were relatively higher in landslide areas compared to that of surrounding non landslide areas the surface roughness index mapped 84 of observed landslides and suggests that the index could be used to map hillslope susceptibility to landslides for future planned studies

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

late alluvial fan formation in southern margaritifer terra mars 1 crater statistics indicate alluvial fans crater floor and fill mantling deposits within impact craters 50 km in diameter in southern margaritifer terra were likely emplaced during multiple epochs fans formed during the amazonian or near the amazonian hesperian boundary crater floor deposits are likely hesperian in age and most fill mantling deposits are amazonian the regional distribution of fans points to a late period of widespread water driven degradation two of the final candidate landing sites for the 2011 mars science laboratory mission would land on or near some of these fans which appear younger than previously considered

timescales of alluvial fan development by precipitation on mars 1 dozens of large low gradient alluvial fans are present within impact crater basins on the cratered highlands of mars the timescales and climate conditions that were required to generate such fans are unknown but testable through our understanding of terrestrial hill slope erosion in the presence of precipitation previous estimates of fan formation time vary from years to millions of years here we use an idealised physical model of 2 d catchment fan evolution to present a framework within which the development of martian alluvial fans should be considered we simplify the erosional and depositional system so that there are only three variables erodibility due to gravity amount of water runoff due to precipitation and catchment fan boundary elevation within this framework to generate large low gradient 108 yr if the substrate is extremely erodible relative to terrestrial examples

insights of dyke emplacement mechanics from detailed 3d dyke thickness datasets abstract dyke thickness datasets offer new insights into the detailed 3d geometry of dyke swarms and an exceptional opportunity to evaluate theoretical emplacement models the swartruggens kimberlite dyke swarm extends over 7 km along strike and intrudes a dolerite quartzite shale and andesitic lava succession the star kimberlite dykes cut shales and sandstones intersect a large dolerite sill and extend 15 km along strike both dyke swarms comprise anastomosing en echelon segments each several hundred metres long in total 1532 swartruggens dyke thickness measurements were taken to 750 m below the surface over a 250 m depth range and 3354 star dyke thickness measurements were taken over a 520 m depth range the swartruggens dyke thicknesses are 0 05 1 95 m mean 0 64 m whereas the star kimberlites range from

methane bursts as a trigger for intermittent lake forming climates on post noachian mars lakes existed on mars later than 3 6 billion years ago according to sedimentary evidence for deltaic deposition the observed fluviolacustrine deposits suggest that individual lake forming climates persisted for at least several thousand years assuming dilute flow but the lake watersheds little weathered soils indicate a largely dry climate history with intermittent runoff events here we show that these observational constraints although inconsistent with many previously proposed triggers for lake forming climates are consistent with a methane burst scenario in this scenario chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate using numerical simulations we find that outgassed methane can build up to atmospheric levels sufficient for lake forming climates if methane clathrate initially occupies more than 4 of the total volume in which it is thermodynamically stable such occupancy fractions are consistent with methane production by water rock reactions due to hydrothermal circulation on early mars we further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake forming climates to less than a million years consistent with observations we conclude that methane bursts represent a potential pathway for intermittent excursions to a warm wet climate state on early mars

gale crater and impact processes curiosity s first 364 sols on mars abstract impact processes at all scales have been involved in the formation and subsequent evolution of gale crater small impact craters in the vicinity of the curiosity msl landing site and rover traverse during the 364 sols after landing have been studied both from orbit and the surface evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate and disrupted fractured sedimentary layers which are not obviously displaced by erosion impact ejecta blankets are likely to be present but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary volcaniclastic breccia and conglomerate deposits the occurrence of individual blocks with diverse petrological characteristics including igneous textures have been identified across the surface of bradbury rise and some of these blocks may represent distal ejecta from larger craters in the vicinity of gale distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material possible examples of impactites in the form of shatter cones shocked rocks and ropy textured fragments of materials that may have been molten have been observed but cannot be uniquely confirmed modification by aeolian processes of craters smaller than 40 m in diameter observed in this study are indicated by erosion of crater rims and infill of craters with aeolian and airfall dust deposits estimates for resurfacing suggest that craters less than 15 m in diameter may represent steady state between production and destruction the smallest candidate impact crater observed is 0 6 m in diameter the observed crater record and other data are consistent with a resurfacing rate of the order of 10 mm myr considerably greater than the rate from impact cratering alone but remarkably lower than terrestrial erosion rates

large alluvial fans on mars 1 several dozen distinct alluvial fans 10 to 40 km long downslope have been observed in highlands craters within a search region between 0 and 30 s alluvial fan containing craters were found only between 18 and 29 s and they all occur at around 1 km of the mola defined martian datum within the study area they are not randomly distributed but instead form three distinct clusters fans typically descend 1 km from where they disgorge from their alcoves longitudinal profiles show that their surfaces are very slightly concave with a mean slope of 2 many fans exhibit very long narrow low relief ridges radially oriented downslope often branching at their distal ends suggestive of distributaries morphometric data for 31 fans were derived from mola data and compared with terrestrial fans with high relief source areas terrestrial low gradient alluvial ramps in inactive tectonic settings and older martian alluvial ramps along crater floors the martian alluvial fans generally fall on the same trends as the terrestrial alluvial fans whereas the gentler martian crater floor ramps are similar in gradient to the low relief terrestrial alluvial surfaces for a given fan gradient martian alluvial fans generally have greater source basin relief than terrestrial fans in active tectonic settings this suggests that the terrestrial source basins either yield coarser debris or have higher sediment concentrations than their martian counterpoints martian fans and terrestrial basin and range fans have steeper gradients than the older martian alluvial ramps and terrestrial low relief alluvial surfaces which is consistent with the construction of martian fans from dominantly gravel sized sediment rather than sand and silt martian fans are relatively large and of low gradient similar to terrestrial fluvial fans rather than debris flow fans although gravity scaling uncertainties make the flow regime forming martian fans uncertain however evidence of bedforms accentuated by differential erosion such as scroll bars supports the contention that these are fluvially formed fans martian fans at least those in holden crater apparently formed around the time of the noachian hesperian boundary we infer that these fans formed during an episode of enhanced precipitation probably snow and runoff which exhibited both sudden onset and termination

alignments of volcanic features in the southern hemisphere of mars produced by migrating mantle plumes abstract mars shows alignments of volcanic landforms in its southern hemisphere starting from the equatorial regions and converging towards the south pole and visible at global scale these composite alignments of volcanoes calderas shields vents heads of valley networks and massifs between the equatorial regions and the southern polar region define twelve different lines fitted by rhumb lines loxodromes that i propose to be the traces of mantle plumes the morphology of the volcanic centres changes along some of the alignments suggesting different processes of magma emplacement and eruptive style the diameters of the volcanic centres and of the volcanic provinces are largest at tharsis and elysium directly proportional to the number of alignments starting from them a minor presence of unaligned volcanic features is observed on the northern lowlands and on the highlands outside the 12 major alignments the heads of channels commonly interpreted as fluvial valleys are aligned with the other volcanic centres unaltered olivine is present along their bed floors raising severe doubts as to their aqueous origin several hypotheses have tried to explain the formation of tharsis with the migration of a single mantle plume under the martian lithosphere but the discovery of twelve alignments six starting from tharsis favours the hypothesis of several mantle plumes as predicted by the model of the southern polar giant impact spgi and provides a new view on the formation of the volcanic provinces of mars

valleys in pit craters on mars characteristics distribution and formation mechanisms abstract new observations of central pit craters on mars reveal that some craters contain prominent interior valley networks that drain into their central pit in this study we catalog the distribution of pit craters with associated valleys and characterize in detail five diverse well preserved examples in some instances sedimentary deposits we interpret as either alluvial fans or deltas are found in the central pits and evidence suggests that at least some of these pits once contained lakes fluvial activity within the five pit craters we detail appears to have occurred relatively late in mars history during the hesperian or amazonian periods for this reason further understanding the formation mechanisms of these valleys has important implications for the history of water on mars

dating very young planetary surfaces from crater statistics a review of issues and challenges determining the ages of young planetary surfaces relies on using populations of small often sub km diameter impact craters due to the higher frequency at which they form smaller craters however can be less reliable for estimating ages as their size frequency distribution is more susceptible to alteration with debate as to whether they should be used at all with the current plethora of meter scale resolution images acquired of the lunar and martian surfaces small craters have been widely used to derive model ages to establish the temporal relation of recent geologic events in this review paper we discuss the many factors that make smaller craters particularly challenging to use and should be taken into consideration when crater counts are confined to small crater diameters establishing confidence in a model age ultimately requires an understanding of the geologic context of the surface being dated as reliability can vary considerably and limitations of the dating technique should be considered in applying ages to any geologic interpretation

late hesperian to early amazonian midlatitude martian valleys evidence from newton and gorgonum basins 1 numerous shallowly incised valleys extend from the upper interior rims of newton and gorgonum basins across smooth interior basin deposits these valleys are a few meters to 300 m wide and may have experienced discharges over all or most of their width implying that they are in fact incised channels in newton crater these valleys extend up to 75 km to near the center of the basin floor in gorgonum basin the valleys terminate at what we interpret to be a former ice covered lake these valleys appear to be examples of scattered shallowly incised valleys found throughout the midlatitudes of mars superimposed upon the widespread mantling deposits within the region on the basis of crater count age dating the interior valleys in newton and gorgonum basins were formed at about the hesperian to amazonian transition the runoff through the valleys may have occurred due to episodic melting of snow and ice that had accumulated on the crater rims temperatures warm enough to cause extensive melting may have occurred during optimal orbital and obliquity configurations because of intensive volcanism releasing greenhouse gasses or as a result of a brief episode of warming from a large impact somewhere on mars the valleys were formed at about the same time as major outflow channels were active along the highlands lowlands boundary water delivered to the northern lowlands by the outflow channels may have been recycled as snow and ice deposits within the martian midlatitudes the episodic melting of such deposits may have formed the midlatitude valleys

layered megablocks in the central uplifts of impact craters abstract a database of bedrock exposed in crater central uplifts has been compiled from multiple orbital datasets in this study we focus on uplifts which show decameter scale layers within the exposed megablocks derived from the bedrock of the preexisting target this distinctive morphology found in 41 craters globally occurs mostly in regions mapped as hesperian plains material generally interpreted as regions of extensive flood lavas the association with volcanic units coupled with morphology and mineralogy that is consistent with flood lava emplacement suggests that the layers are stacks of dense lava interbedded with weaker materials estimates for the uplift of stratigraphic sections coupled with morphologic and morphometric analyses lead to estimated thicknesses of the layered unit these estimates indicate hesperian flood lavas are 23 thicker than a previous minimum estimate with a volume of 5 5 10 7 km 3 this increases the known extrusive volcanic production for the history of mars and volatile release to past martian atmospheres

pacing early mars river activity embedded craters in the aeolis dorsa region imply river activity spanned 1 20 myr we find net sedimentation rate 13 200 m yr in the aeolis dorsa region mars using the frequency of crater river interactions this sets a lower bound of 1 20 myr on the total interval spanned by fluvial activity which we correlate to the noachian hesperian transition the main uncertainty is the impact flux at the time of deposition this result rules out basin filling by a single catastrophic episode such as a single impact induced water vapor greenhouse

influence of crystallised igneous intrusions on fault nucleation and reactivation during continental extension abstract continental rifting is commonly accommodated by the nucleation of normal faults slip on pre existing fault surfaces and or magmatic intrusion because crystallised igneous intrusions are pervasive in many rift basins and are commonly more competent i e higher shear strengths and young s moduli than the host rock it is theoretically plausible that they locally intersect and modify the mechanical properties of pre existing normal faults we illustrate the influence that crystallised igneous intrusions may have on fault reactivation using a conceptual model and observations from field and subsurface datasets our results show that igneous rocks may initially resist failure and promote the preferential reactivation of favourably oriented pre existing faults that are not spatially associated with solidified intrusions fault segments situated along strike from laterally restricted fault intrusion intersections may similarly be reactivated this spatial and temporal control on strain distribution may generate 1 supra intrusion folds in the hanging wall 2 new dip slip faults adjacent to the igneous body or 3 sub vertical oblique slip faults oriented parallel to the extension direction importantly stress accumulation within igneous intrusions may eventually initiate failure and further localise strain the results of our study have important implications for the structural of sedimentary basins and the subsurface migration of hydrocarbons and mineral bearing fluids

recent aqueous environments in martian impact craters an astrobiological perspective the discovery of gullies and debris aprons raises the question of the existence of aqueous environments on mars in recent geological times and its astrobiological implications three cases of such environments are surveyed at moc high resolution in the e gorgonum chaos and newton and hale craters the regional setting of these craters suggests that the mechanisms of aquifer destabilization flow discharge and gully formation in these three cases result from local geological triggers that can include impact cratering and tectonic processes rather than climate or insolation factor we take as a working hypothesis that microbial life appeared on mars in ancient geological times probably in a geothermal environment but potentially evolving via infrared detection systems to give photosynthetic communities under the selective pressure of energetic solar radiation we hypothesize that some microbial communities could have survived underground in either dormant or active state or that their biomolecules could be preserved either frozen or desiccated in the subsurface beneath the upper oxidized zone we assess the known environmental constraints for life and what type of potential habitats are provided in these three craters by aquifer discharges using comparison with terrestrial analogues and their associated microbial communities these environments include 1 the release of water on a dry crater floor in e gorgonum and the possibility for microorganisms and preserved biomolecules to be flushed out and mixed in with the sediment exposed at the surface 2 the evidence of a recent lacustrine episode in the newton crater with analogy to antarctic dry valley lakes 3 the exposure on the floor of hale crater of material from a regional subsurface that is likely to have retained traces of one of the oldest martian bodies of water recognized to date parker et al 2000 in the argyre basin we show how the water in argyre 3 8 billion years ago gya was likely to have been alterated by hydrothermal processes and how the subsequent formation of the 150 km hale crater on the northern ring of argyre generated hydrothermal pumping this accounts for the anomalously high location of the springs on the crater crests today with respect to the rest of the regional subsurface distribution finally we envision current impact cratering as a factor for destabilizing aquifers on mars today thus creating new environments we analyze the implications of impacts for two geological types of rock units that could harbor traces of life as a result we compare the potential of astrobiological exploration of crater floors rims and ejecta on future missions to mars

the origin and evolution of the peace vallis fan system that drains to the curiosity landing area gale crater mars the landing site for the curiosity rover is located at the distal end of the peace vallis fan in gale crater peace vallis fan covers 80 km2 and is fed by a 730 km2 catchment which drains an upland plains area through a 15 km wide gap in the crater rim valley incision into accumulated debris delivered sediment through a relatively low density valley network to a main stem channel to the fan an estimated total fan volume of 0 9 km3 matches the calculated volume of removal due to valley incision 0 8 km3 and indicates a mean thickness of 9 m the fan profile is weakly concave up with a mean slope of 1 5 for the lower portion numerous inverted channels outcrop on the western surface of the fan but on the eastern portion such channels are rare suggesting a change in process from distributary channel domination on the west to sheet flow on the eastern portion of the fan runoff discharge watershed area to produce the fan is estimated to be more than 600 m perhaps as much as 6000 m indicating a hydrologic cycle that likely lasted at least thousands of years atmospheric precipitation possibly snow not seepage produced the runoff based on topographic data peace vallis fan likely onlapped bradbury rise and spilled into a topographic low to the east of the rise this argues that the light toned fractured terrain within this topographic low corresponds to the distal deposits of peace vallis fan and in such a setting lacustrine deposits are expected

aspect related microclimatic influences on slope forms and processes northeastern arizona 1 climate is a major control on geomorphology yet the effects of aspect related differences in microclimate have been little studied we examined several 60 100 m deep canyons in semiarid northeastern arizona where rock type and structure are essentially constant but where field data and a high resolution digital elevation model reveal consistent morphologic and microclimatic differences between asymmetric north and south facing sideslopes cliffs account for 29 of the vertical relief of south facing slopes but only 2 5 of north facing slopes excluding cliffs south facing slopes are 1 3 steeper than north facing slopes and have significantly less weathered bedrock we monitored air surface and subsurface temperatures and soil moisture at 0 5 h intervals at four locations over 1 year south facing slopes were 1 4 5 6 c warmer and soil moisture tension at 10 cm depth averages at least 78 kpa lower drier than on north facing slopes the dominant rock type in the study area morrison formation sandstone weathers primarily by clay hydration these sandstones form disaggregated mantles where weathering exceeds erosion but also maintain steep slopes and cliffs where little weathered south facing slopes were too dry during most of the instrumented year for significant clay expansion whereas the north facing bedrock slope was moist all year cliff growth thus occurs preferentially on warmer and drier slopes where weathering is reduced small north facing cliffs typically 3 m could have formed during the holocene but cliffs up to 70 m high on southerly aspects require more time to form and likely persisted or expanded under cooler and wetter late pleistocene climates

the timing of alluvial activity in gale crater mars the curiosity rover s discovery of rocks preserving evidence of past habitable conditions in gale crater highlights the importance of constraining the timing of responsible depositional settings to understand the astrobiological implications for mars crater statistics and mapping reveal the bulk of the alluvial deposits in gale including those interrogated by curiosity were likely emplaced during the hesperian thereby implying that habitable conditions persisted after the noachian crater counting data sets and upper peace vallis fan morphology also suggest a possible younger period of fluvial activation that deposited 10 20 m of sediments on the upper fan after emplacement of the main body of the fan if validated water associated with later alluvial activity may have contributed to secondary diagenetic features in yellowknife bay

sequence and relative timing of large lakes in gale crater mars after the formation of mount sharp the quantification of lake levels in gale crater is important to define the hydrologic and climatic history experienced by the sedimentary deposits found by curiosity we propose that there were at least three major lake stands within gale each persisted 1000 years and all occurred after mount sharp reached close to its current topographic form deltaic deposits off the southern rim of gale derived from incision of farah vallis and corresponding deposits off the southern flank of mount sharp define the highest lake level which had a mean depth of 700 m canyons similar in form to farah vallis enter into craters and or the crustal dichotomy near gale from the south suggesting that the highest lake was supplied by a large scale flow system the next lake level established after a period of drying and rewetting is defined by four deltaic features three sourced from mount sharp and one from the western rim of gale as well as the termination of gullies around the northern rim of gale this second lake level had a mean depth of 300 m the presence of the gullies suggests more locally sourced water lake levels then rose another 100 m as evidenced by two deltaic deposits derived from the rim of gale and the termination of a second set of gullies post lake reduced hydrologic activity continued evidenced by a time of fan building including peace vallis the sequence of events suggests an episodic shift through time from relatively wet regional conditions to a drier environment with local runoff

temporal and spatial climatic controls on holocene fire related erosion and sedimentation jemez mountains new mexico in the jemez mountains tree ring data indicate that low severity fires characterized the 400 yr before euro american settlement and that subsequent fire suppression promoted denser forests recent severe fires and erosion over longer timescales climate change may alter fire regimes thus we used fire related alluvial deposits to assess the timing of moderate to high severity fires their geomorphic impact and relation to climate over the last 4000 yr fire related sedimentation does not clearly follow millennial scale climatic changes but probability peaks commonly correspond with severe drought e g within the interval 1700 1400 cal yr bp and ca 650 and ca 410 cal yr bp the latter episodes were preceded by prolonged wet intervals that could promote dense stands estimated recurrence intervals for fire related sedimentation are 250 400 yr climatic differences with aspect influenced holocene post fire response fire related deposits constitute 77 of fan sediments from north facing basins but only 39 of deposits from drier southerly aspects with sparser vegetation and exposed bedrock south aspects can generate runoff and sediment when unburned whereas soil mantled north aspects produce minor sediment unless severely burned recent channel incision appears unprecedented over the last 2300 yr suggesting that fuel loading and extreme drought produced an anomalously severe burn in 2002

ecohydrologic role of solar radiation on landscape evolution solar radiation has a clear signature on the spatial organization of ecohydrologic fluxes vegetation patterns and dynamics and landscape morphology in semiarid ecosystems existing landscape evolution models lems do not explicitly consider spatially explicit solar radiation as model forcing here we improve an existing lem to represent coupled processes of energy water and sediment balance for semiarid fluvial catchments to ground model predictions a study site is selected in central new mexico where hillslope aspect has a marked influence on vegetation patterns and landscape morphology model predictions are corroborated using limited field observations in central nm and other locations with similar conditions we design a set of comparative lem simulations to investigate the role of spatially explicit solar radiation on landscape ecohydro geomorphic development under different uplift scenarios aspect control and network control are identified as the two main drivers of soil moisture and vegetation organization on the landscape landscape scale and long term implications of these short term ecohdrologic patterns emerged in modeled landscapes as north facing slopes nfs get steeper by continuing uplift they support erosion resistant denser vegetation cover which leads to further slope steepening until erosion and uplift attains a dynamic equilibrium conversely on south facing slopes sfs as slopes grow with uplift increased solar radiation exposure with slope supports sparser biomass and shallower slopes at the landscape scale these differential erosion processes lead to asymmetric development of catchment forms consistent with regional observations understanding of ecohydrogeomorphic evolution will improve to assess the impacts of past and future climates on landscape response and morphology

3d morphometry of valley networks on mars from hrsc mex dems implications for climatic evolution through time 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands eight dense branching valley networks were studied in noachian terrains of huygens newcomb and kepler craters south tyrrhena terra and thaumasia in hesperian terrains of echus plateau and west eberswalde craters and in amazonian terrains of alba patera using images and digital elevation models from the mars express high resolution stereo camera to determine 2d and 3d morphometric parameters extracted geomorphic parameters show similar geometry to terrestrial valleys drainage densities organization from bifurcation ratios and lengths ratios hack exponent consistent with terrestrial values of 0 6 and progressive deepening of valleys with increasing strahler order in addition statistics on valley depths indicate a deeper incision of noachian valleys compared to younger post noachian valleys 100 m for noachian ones showing a strong difference in fluvial erosion these characteristics show that dense martian valley networks formed by overland flows in relation to a global atmospheric water cycle in noachian epoch and confirm that the later stages of activity may be related to shorter duration of activity distinct climatic conditions and or regional processes or conditions

the influence of climate and microclimate aspect on soil creep efficiency cinder cone morphology and evolution along the eastern mediterranean golan heights although hillslope evolution has been subject to much investigation for more than a century the effect of climate on the morphology of soil mantled hillslopes remains poorly constrained in this study we perform numerical simulations of volcanic cinder cones in the golan heights eastern mediterranean to estimate soil transport efficiency across a significant north south gradient in mean annual precipitation 1100 to 500 mm we use the initial cinder cone morphology constrained by stratigraphy the modern hillslope form surveyed with sub meter accuracy and the eruption age based on 40ar 39ar chronology to predict the best fit value of the soil transport coefficient diffusivity based on a nonlinear transport model our results indicate that the best fit diffusivity k varies from 1 to 6 m2 ka 1 among the five cinder cones in our field area diffusivity k values vary systematically with precipitation and hillslope aspect specifically k is higher on south facing drier hillslopes and decreases with mean annual precipitation we interpret this climate dependency to reflect vegetation driven variations in apparent soil cohesion which increases with root network density and attenuation of rain splash and overland flow erosion which increases with vegetative ground cover to assess how vegetative root mass and ground cover vary with precipitation and aspect we quantified the spatial distribution of ndvi normalized difference vegetation index from aster satellite images and observed spatial variations that correlate with our calibrated values of k analysis of previously studied cinder cones in the usa can be used to extend our framework to arid domains this endeavor suggests a humped relationship between k and precipitation with maximum diffusivity at mean annual precipitation of 400 600 mm copyright 2017 john wiley sons ltd

a geomorphic analysis of hale crater mars the effects of impact into ice rich crust abstract hale crater a 125 150 km impact crater located near the intersection of uzboi vallis and the northern rim of argyre basin at 35 7 s 323 6 e is surrounded by channels that radiate from incise and transport material within hale s ejecta the spatial and temporal relationship between the channels and hale s ejecta strongly suggests the impact event created or modified the channels and emplaced fluidized debris flow lobes over an extensive area 200 000 km2 we estimate 1010 m3 of liquid water was required to form some of hale s smaller channels a volume we propose was supplied by subsurface ice melted and mobilized by the hale forming impact if 10 of the subsurface volume was ice based on a conservative porosity estimate for the upper martian crust 1012 m3 of liquid water could have been present in the ejecta we determine a crater retention age of 1 ga inside the primary cavity providing a minimum age for hale and a time at which we propose the subsurface was volatile rich hale crater demonstrates the important role impacts may play in supplying liquid water to the martian surface they are capable of producing fluvially modified terrains that may be analogous to some landforms of noachian mars

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

valley asymmetry and glacial versus nonglacial erosion in the bitterroot range montana usa theories that propose feedbacks among climate tectonics and surface processes commonly assume that erosion is enhanced by glacial activity indeed studies have shown that glaciers appear to limit the elevation of mountain ranges however comparisons between rates of glacial and nonglacial erosion are difficult to make ideally such comparisons must hold precipitation and lithology constant while only varying the erosional regime located in a climatic transition zone during the pleistocene the east west trending valleys of the bitterroot range present an opportunity for a quantitative analysis of glacial and nonglacial erosion because the north facing sides of the valleys were glaciated whereas the south facing slopes were not the different erosional regimes operating on either side of the valleys created strongly asymmetric ridges ridgelines separating the east west trending valleys have been pushed southward by glacial headwall retreat such that ridge to valley distances are 50 greater on the north facing slopes than on the south facing slopes in addition mean hillslope angles are 6 lower on the glaciated slopes than on the unglaciated slopes and calculations of geophysical relief suggest that on average glaciers have removed nearly twice as much rock as nonglacial processes finally we conclude that although rates of vertical incision by glacial processes in the bitterroot range were more rapid than nonglacial processes the dominant geomorphological impact of glaciers was lateral erosion by headwall retreat

aspect dependent variations in regolith creep revealed by meteoric 10be although variations in insolation and emergent feedbacks among soil moisture vegetation and soil cohesion are commonly invoked to explain topographic asymmetry that depends on aspect few studies have directly quantified the efficiency of regolith transport along hillslopes of opposing aspect we utilize meteoric 10 be concentrations in regolith n 74 to determine mass flux along equatorial facing and polar facing hillslopes in three forested upland watersheds in and adjacent to the susquehanna shale hills critical zone observatory in central pennsylvania usa in combination with regolith depth measurements and high resolution topography these fluxes allow us to evaluate transport rate laws and the efficiency of regolith creep concentrations of meteoric 10 be in regolith along six separate transects imply that regolith flux is similar along all hillslopes despite differences in topographic gradient and regolith thickness comparison of flux with regolith depth and topographic gradient reveals that transport depends on regolith depth and that regolith creep is twice as efficient along low gradient south facing slopes with thin regolith as compared to steep north facing slopes mantled with thicker regolith we suggest that the observed topographic asymmetry in these watersheds has evolved over geologic time as a result of differences in the frequency of freeze thaw events between hillslopes of opposing aspect

hillslope asymmetry maps reveal widespread multi scale organization 1 hillslope asymmetry is the condition in which oppositely facing hillslopes within an area have differing average slope angles and indicates aspect related variability in hillslope evolution as such the presence orientation and magnitude of asymmetry may be a useful diagnostic for understanding process dominance we present a new method for quantifying and mapping the spatial distribution of hillslope asymmetry across large areas resulting maps for the american cordillera of the western hemisphere and the western united states reveal that hillslope asymmetry is widespread with distinct trends at continental to drainage scales spatial patterns of asymmetry correlate with latitude along the american cordillera mountain range orientation for many ranges in the western united states and elevation in the idaho batholith of the northern rocky mountains spatial organization suggests that non stochastic process driven controls cause these patterns the hillslope asymmetry metric objectively captures previously documented extents and frequencies of valley asymmetry for the gabilan mesa of the central california coast range broad scale maps of hillslope asymmetry are of interest to a wide range of disciplines as spatial patterns may reflect the influence of tectonics atmospheric circulation topoclimate geomorphology hydrology soils and ecology on landscape evolution these maps identify trends and regions of hillslope asymmetry allow possible drivers to be spatially constrained and facilitate the extrapolation of site specific results to broader regions

chemical variations in yellowknife bay formation sedimentary rocks analyzed by chemcam on board the curiosity rover on mars the yellowknife bay formation represents a similar to 5m thick stratigraphic section of lithified fluvial and lacustrine sediments analyzed by the curiosity rover in gale crater mars previous works have mainly focused on the mudstones that were drilled by the rover at two locations the present study focuses on the sedimentary rocks stratigraphically above the mudstones by studying their chemical variations in parallel with rock textures results show that differences in composition correlate with textures and both manifest subtle but significant variations through the stratigraphic column though the chemistry of the sediments does not vary much in the lower part of the stratigraphy the variations in alkali elements indicate variations in the source material and or physical sorting as shown by the identification of alkali feldspars the sandstones contain similar relative proportions of hydrogen to the mudstones below suggesting the presence of hydrous minerals that may have contributed to their cementation slight variations in magnesium correlate with changes in textures suggesting that diagenesis through cementation and dissolution modified the initial rock composition and texture simultaneously the upper part of the stratigraphy similar to 1m thick displays rocks with different compositions suggesting a strong change in the depositional system the presence of float rocks with similar compositions found along the rover traverse suggests that some of these outcrops extend further away in the nearby hummocky plains

impact crater lakes on mars the robotic search for life on mars centers on identifying accessible environments where the biological catalyst water has existed the formation of large impact craters on mars 65 km diameter may have resulted in the creation of ice covered impact crater lakes which would not freeze for thousands of years even under present climatic conditions water could be supplied from deep confined aquifers penetrated by the impact craters without the need for surface melt water freezing of the lakes is postponed owing to heat from impact generated melt bearing deposits from impact related uplift of hotter rocks from depth and from the latent heat of freezing of a deep crater lake abundant morphologic evidence for ancient crater lakes has not been found in viking images except for craters associated with outflow channels however ice covered crater lakes could have formed and further searches for evidence of these lakes are warranted the lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from mars

stepped fans and facies equivalent phyllosilicates in coprates catena mars stepped fan deposits and phyllosilicate mineralogies are relatively common features on mars but have not previously been found in association with each other both of these features are widely accepted to be the result of aqueous processes but the assumed role and nature of any water varies in this study we have investigated two stepped fan deposits in coprates catena mars which have a genetic link to light toned material that is rich in fe mg phyllosilicate phases although of different sizes and in separate but adjacent trough like depressions we identify similar features at these stepped fans and phyllosilicates that are indicative of similar formation conditions and processes our observations of the overall geomorphology mineralogy and chronology of these features are consistent with a two stage formation process whereby deposition in the troughs first occurs into shallow standing water or playas forming fluvial or alluvial fans that terminate in delta deposits and interfinger with interpreted lacustrine facies with a later period of deposition under sub aerial conditions forming alluvial fan deposits we suggest that the distinctive stepped appearance of these fans is the result of aeolian erosion and is not a primary depositional feature this combined formation framework for stepped fans and phyllosilicates can also explain other similar features on mars and adds to the growing evidence of fluvial activity in the equatorial region of mars during the hesperian and amazonian

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

influence of fault controlled topography on fluvio deltaic sedimentary systems in eberswalde crater mars 1 eberswalde crater was selected as a candidate landing site for the mars science laboratory msl mission based on the presence of a fan shaped sedimentary deposit interpreted as a delta we have identified and mapped five other candidate fluvio deltaic systems in the crater using images and digital terrain models dtms derived from the mars reconnaissance orbiter mro high resolution imaging science experiment hirise and context camera ctx all of these systems consist of the same three stratigraphic units 1 an upper layered unit conformable with 2 a subpolygonally fractured unit unconformably overlying 3 a pitted unit we have also mapped a system of nne trending scarps interpreted as dip slip faults that pre date the fluvial lacustrine deposits the post impact regional faulting may have generated the large scale topography within the crater which consists of a western basin an eastern basin and a central high this topography subsequently provided depositional sinks for sediment entering the crater and controlled the geomorphic pattern of delta development

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

the origin and timing of fluvial activity at eberswalde crater mars the fan deposit in eberswalde crater has been interpreted as strong evidence for sustained liquid water on early mars with a paleolake formed during the noachian period 3 7 gy this location became a key region for understanding the mars paleo environment eberswalde crater is located 50 km north of the rim of the 150 km diameter crater holden stratigraphic relationships and chronology obtained using recent mars express high resolution stereo camera and mars reconnaissance orbiter context camera images show that eberswalde fluvial activity crosscuts holden ejecta and thus postdates holden crater whose formation age is estimated from crater counts as late hesperian 3 5 gy depending on models fluvial modeling shows that short term activity over several years to hundreds of years involving dense flows with sediment water ratio between 0 01 and 0 3 may be as good an explanation of the fluvial landforms as dilute flow over longer durations modeling of the thermal effect of the holden impact in the eberswalde watershed is used to evaluate its potential role in aqueous activity the relative timing of the holden impact and eberswalde s fan is a constraint for future studies about the origin of these landforms holden ejecta form a weak and porous substrate which may be easy to erode by fluvial incision in a cold climate scenario impact heating could have produced runoff by melting snow or ground ice any attempt to model fluvial activity at eberswalde should take into account that it may have formed as late as in the late hesperian after the great majority of valley network formation and aqueous mineralization on mars this suggests that hypotheses for fan formation at eberswalde by transient and or localized processes i e impact volcanism unusual orbital forcing should be considered on a par with globally warmer climate

morphometry of great basin pluvial shore landforms implications for paleolake basins on mars 1 many basins with relict contributing valley networks and outlet valleys in the martian highlands indicate past flowing and ponded water on the surface these likely paleolakes motivate an investigation of pluvial shore landforms in the great basin region of the western united states as confident identification of strandlines on mars would facilitate analyses of its past hydrology and climate the purpose of this study is to characterize the scale of late pleistocene erosional and depositional shore landforms in an endorheic setting determine the preservation potential of similar forms from multiple epochs in early martian history and identify the data products that would be necessary to detect them we use differential global positioning system field surveys to measure the dimensions and elevations of shore landforms compare shore platform widths to theoretical maxima and note the minimum scale of landforms that have survived since the late noachian and early hesperian epochs on mars we find that due to impact gardening and aeolian erosion martian highland paleolakes like those in the pluvial great basin would likely not have well preserved shore landforms unless they were unusually large and formed in the late hesperian or later individual strandlines are often not equally well expressed around an entire basin so correlating shore landforms in plan view imaging and using their consistency in elevation as a hypothesis test for paleolakes can be challenging detection of younger shore landforms like those examined here would require meter resolution imaging and topography such as stereo digital elevation models

catalogue of large alluvial fans in martian impact craters abstract we conducted a systematic global survey using thermal emission imaging system infrared themis ir coverage 100 m pixel to search for large alluvial fans in impact craters on mars our survey has focused on large fans apron areas greater than 40 km 2 usually located in craters greater than 20 km in diameter due to the resolution of the themis images and mars orbiter laser altimeter mola coverage we find that the host craters are found to have a distinctive diameter range from 30 150 km the fans generally cluster in three geographic areas southern margaritifer terra southwestern terra sabaea and southwestern tyrrhena terra however several outliers do exist the alluvial fans do not form in a particular orientation along the crater rim nor are they associated with the location of current high rim topography fan area magnitude and variability increase with crater diameter while fan concavity magnitude and variability increase with decreasing crater diameter smaller fan aprons in general have higher more variable concavity the source of the water forming these fans is uncertain given the challenges of accommodating the global distribution pattern and formation patterns within the craters

minimum effective area for high resolution crater counting of martian terrains the acquisition of high resolution imagery for the surface of mars has enabled mapping of spatially limited order of 200 m on four type terrains using mars reconnaissance orbiter mro context camera ctx imagery that span the noachian hesperian and amazonian epochs the counts from each location include a region covering 10 000 km2 ten 1000 km2 subsets of that larger area and approximately one hundred 100 km2 samples the data demonstrate significant variation in the crater size frequency and derived model ages across a single terrain type for the 100 km2 samples the crater size frequency at this area scale varies across a single uniform geologic unit by up to a factor of 2 3 on the four different terrains at 1000 km2 the local pattern variations that are relevant at the 100 km2 scale become less important and the age variations are tighter in all four terrain cases the 10 000 km2 and 1000 km2 samples capture distinct crater populations km sized craters that formed before and after resurfacing event s however due to the relatively high mean distance between km sized craters the 100 km2 size area samples more commonly than not exclude a statistically significant sample at the kilometer size range masking important information about the pre resurfacing history of the terrain we therefore suggest that due to the effect of pattern variability in cratering over 100 km2 and the susceptibility of smaller craters to resurfacing crater counts derived from small area samples are suspect to major uncertainties

evidence for episodic alluvial fan formation in far western terra tyrrhena mars a late noachian aged alluvial fan complex within harris crater in far western terra tyrrhena mars is comprised of two well defined source regions and associated discrete depositional lobes three fan units were recognized based on common morphological characteristics thermal properties and spectral signatures although the entire fan complex has been subjected to extensive erosional degradation the preserved morphologies record episodic fan formation and indicate the type of flow processes that occurred the bulk of the fan surface has morphology consistent with fluvial emplacement while one fan unit exhibits a rugged surface texture with boulders consistent with a debris flow this transition from fluvial to late stage debris flow s suggests a decline in available water and or change in sediment supply the thermal inertia values obtained for all three fan surface units mean values ranged from 318 to 344 j m 2 k

hirise imaging of impact megabreccia and sub meter aqueous strata in holden crater mars high resolution imaging science experiment hirise images of holden crater mars resolve impact megabreccia unconformably overlain by sediments deposited during two noachian age phases of aqueous activity a lighter toned lower unit exhibiting phyllosilicates was deposited in a long lived quiescent distal alluvial or lacustrine setting an overlying darker toned and often blocky upper unit drapes the sequence and was emplaced during later high magnitude flooding as an impounded uzboi vallis lake overtopped the crater rim the stratigraphy provides the first geologic context for phyllosilicate deposition during persistent wet and perhaps habitable conditions on early mars

drainage and valley asymmetry in the tertiary hills of lower bavaria germany abstract valley asymmetry with steeper west facing valley sides is a common feature in the tertiary hills of lower bavaria several previous studies have attributed these forms to microclimatic differences under periglacial conditions during the pleistocene glacials however little attention has been given to the pattern of drainage networks in this area as a means of explaining valley asymmetry drainage networks show asymmetry both in length and number of tributaries on either side of the main stream drainage asymmetry is very likely primarily the reason of a drainage development in competitive situations four possible causes have been identified 1 the position of an initial channel in relation to its adjacent parallel or subparallel drainage lines 2 different rates of headward erosion of tributaries on either side of an inter stream divide 3 drainage development oblique to an initial terrain slope and 4 tilting of a landsurface and the resulting preferential headward erosion of consequent running streams thus asymmetric drainage development causes differences in slope dimensions and an imbalance in run off and sediment yield on opposite valley sides leading to the development of asymmetric valleys

evidence for a short period of hydrologic activity in newton crater mars near the hesperian amazonian transition 1 hesperian amazonian aged valleys and alluvial fans distributed in regional clusters throughout the southern middle to low latitudes were formed during a period of fluvial runoff and erosion which acted over a smaller spatial and temporal scale than the older classical martian valley networks dated to the noachian hesperian boundary in order to explore the potential sources of water which formed these younger valleys we calculated the expected sediment transport and water discharge rates for a valley and alluvial fan located in newton crater 40 s 159 e over a wide range of water filled channel depths and sediment grain sizes in order to constrain the formation timescale and required water volume depending on the depth of the water filled channel within the valley the alluvial fan was likely emplaced over 0 1 to 10 years of fluvial activity involving between 1 8 and 5 7 km 3 of water these results imply water runoff rates of between 1 and 10 cm d over a typical 300 km2 drainage area possible processes for delivering water to these drainages include high obliquity snowpack melting via volcanism or impacts resulting in either scattered local to regional melting events or a brief global warming event an extended perhaps episodic period of fluvial activity lasting hundreds of years driven by insolation induced melting of high obliquity snowpacks is another possibility

computer generated global map of valley networks on mars 1 the presence of valley networks vn on mars suggests that early mars was warmer and wetter than present however detailed geomorphic analyses of individual networks have not led to a consensus regarding their origin an additional line of evidence can be provided by the global pattern of dissection on mars but the currently available global map of vn compiled from viking images is incomplete and outdated we created an updated map of vn by using a computer algorithm that parses topographic data and recognizes valleys by their morphologic signature this computer generated map was visually inspected and edited to produce the final updated map of vn the new map shows an increase in total vn length by a factor of 2 3 a global map of dissection density d derived from the new vn map shows that the most highly dissected region forms a belt located between the equator and mid southern latitudes the most prominent regions of high values of d are the northern terra cimmeria and the margaritifer terra where d reaches the value of 0 12 km 1 over extended areas the average value of d is 0 062 km 1 only 2 6 times lower than the terrestrial value of d as measured in the same fashion these relatively high values of dissection density over extensive regions of the planet point toward precipitation fed runoff erosion as the primary mechanism of valley formation assuming a warm and wet early mars peculiarity of the global pattern of dissection is interpreted in the terms of climate controlling factors influenced by the topographic dichotomy