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

age dates of valley network drainage basins and subbasins within sabae and arabia terrae mars the precise timing of valley network drainage basin formation is critical to understanding the history of water and climate on mars to determine whether there are any variations in ages within separate drainage basins and subbasins that may reflect local or regional variations in climate or resetting from resurfacing e g impact ejecta or lava flows we dated 27 basins and subbasins in sabaea and arabia terrae the age dating basin technique we employed allowed sufficient precision to give accurate ages and shows that fluvial activity within the basins and subbasins ceased at approximately the same time around the early hesperian late hesperian transition our results support the hypothesis that valley networks formed during a unique fluvial optimum that may have shut off gradually because of a global climate change that affected all areas simultaneously on mars

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

age and evolution of the lower nw flank of the hecates tholus volcano mars based on crater size frequency distribution on ctx images abstract we present results of crater size frequency distribution sfd analysis of the lower nw flank of the hecates tholus volcano elysium volcanic province of mars by the use of images acquired by the context ctx instrument on board of mars reconnaissance orbiter 6 m pixel in resolution previous similar works were focused on the caldera complex of the volcano and some sectors of the lower nw flank in this study we analyzed the complete crater population of the main geomorphological units characterizing this sector of the volcano de pablo m a centeno j d 2012 journal of maps 8 3 208 2014 discarding areas with possible clustering to avoid erroneous results in total 16 areas corresponding to 10 geomorphological units were measured and absolute model ages were derived for them the ages correspond to ages of origin as well as of the end of resurfacing events depending on the analyzed sector resulting in some cases in more than one age per area our results are in general in agreement with previous works and establish that the age of the origin of the hecates tholus volcano could be at least 3 8 ga with possible volcanic eruptions occurring until at least 335 ma glacial events were also dated at 90 ma 30 ma 16 ma and 6 ma although it is possible to recognize ages which could also be related to the recent ice ages of mars between 2 and 0 4 ma our results allowed us to determine that glacial processes could have been active as far back as 1 4 ga with possible events at intermediate ages we deduced from the resulting ages and our observations on ctx images and the available geomorphological map of the area that glacial related processes played an important role in sculpting this flank of the volcano and the possible level of the glacial sheet at the edge of the main depression of this flank was also deduced with altitudes ranging between 2035 m and 2490 m in agreement with the presence of smooth outcrops and roche moutonnees in the area finally a possible evolution of this region of the hecates tholus volcano is proposed and discussed establishing the sequence of the most important geological events which occurred in the area and their possible timings

complex evolution of paleolacustrine systems on mars an example from the holden crater 1 the 150 km wide holden crater lies in an area characterized by high density of valley networks implying conditions conducive to forming of water related environments we undertook geological mapping and a stratigraphic survey in order to probe the evolution of water related landforms and their paleoenvironmental implications our investigations lead us to propose that the holden area was subjected to a wet lacustrine phase of hesperian age and an icy phase during the amazonian deltaic coastal and lacustrine environments occurred during the wet phase some displaying a cyclic depositional pattern presumably related to autogenic processes water was delivered to the basin by the uzboi vallis and by surface runoff channels from a series of drainage basins along the crater walls fan delta geometries and coastal onlap enabled estimation of major water levels two levels of major stand of the water have been recognized possibly reflecting allogenic controls geologic units related to this wet lacustrine phase were subsequently eroded by glacial abrasion and plucking and were disconformably overlain by glacial deposits of amazonian age defining an icy phase these features are consistent with a warm based glacier entering the holden crater through the wide uzboi vallis to form a proglacial lake in the central part of the crater changes in sedimentary units reflect changes of depositional environments probably connected with climatic variation

watershed modeling in the tyrrhena terra region of mars 1 watershed analyses from high resolution image viking mars orbiter camera and thermal emission imaging system and topographic mars orbiter laser altimeter mola data are used to qualitatively and quantitatively characterize highland fluvial systems and analyze the role of water in the evolution of tyrrhena terra 13 s 30 s 265 w 280 w mars in this study geographical information system software is used in conjunction with mola digital elevation models to delineate drainage basin divides extract valley networks and derive basin and network morphometric parameters e g drainage density stream order bifurcation ratio and relief morphometry useful in characterizing the geologic and climatic conditions of watershed formation as well as for evaluating basin maturity and processes of watershed development model predicted valley networks and watershed boundaries which are dependent on the degree to which pixel sinks are filled in the topographic data set and a channelization threshold are evaluated against image and topographic data slope maps and detailed maps of valley segments from photogeologic analyses valley morphologies crater valley relationships and impact crater distributions show that valleys in tyrrhena terra are ancient based on geologic properties of the incised materials valley and network morphologies morphometric parameters and the presence of many gullies heading at or near crater rim crests surface runoff derived from rainfall or snowmelt was the dominant erosional process sapping may have only played a secondary role in valley formation in tyrrhena terra furthermore spatial and temporal relationships of dissected highland materials and impact craters suggests widespread but relatively short lived erosion by runoff with most activity in the noachian period

gravity inferred crustal attributes of visible and buried impact basins on mars 1 the impact basins of mars reveal important insights on martian tectonic evolution they involve strongly disrupted depressed regions of crust with likely enhanced porosity and permeability that may locally concentrate water and other crustal fluids hence the crustal properties of impact basins can also be important in the hunt for water and related clues for life on mars we assess the crustal details of impact basins by separating the mars global surveyor free air anomalies into terrain correlated and terrain decorrelated components the separation is based on the correlation spectrum between the free air anomalies and the gravity effects evaluated from the topography mapped by the mars orbital laser altimeter mola for topographically visible multiring basins like isidis striking circular patterns of alternating terrain correlated free air maxima and minima mark the uncompensated components of the central mantle plug and surrounding rings the first vertical derivatives of these anomalies effectively estimate the basin ring locations and a transient cavity depth to diameter ratio of 0 09 that is consistent with the ratio observed for lunar nearside multiring basins for the isidis basin we obtain an excavation depth of roughly 66 km that reflects considerably disrupted crust for concentrating local fluids since the noachian impact furthermore the related crustal terrain decorrelated free air anomalies suggest up to 2 km of high density basin fill may cap the central basin subtle quasi circular depressions in the relatively featureless mola terrain of the northern hemisphere have identified potentially buried impact basins frey et al 2002 an altimetry depression in acidalia planitia and another in utopia are also associated with ringed patterns of terrain decorrelated free air anomalies that may mark the uncompensated mass effects of buried impact basins the gravity derived transient excavation depths for these inferred basins are roughly 41 and 20 km respectively while the related ring diameters d follow the ubiquitous d rule of planetary impact basins the crust of these buried basins is likely to contain water at higher levels than the crust of the equatorial basins that was substantially dewatered with the development of the great northern basin hence analyzing surface fractures faults and other crustal discontinuities that can tap the more saturated crust of these inferred buried basins may facilitate the hunt for water on mars

biogeomorphology revisited looking towards the future although biogeomorphological research is well established with many studies on a range of two way interrelations between organisms and geomorphology in different environments there is little consensus over what constitutes biogeomorphology why it might be useful and where it is heading starting with definitions of core biogeomorphic processes we consider the need for future biogeomorphological studies to evaluate the crucial links between bioprocesses biological community dynamics and inorganic earth surface processes five key applications of biogeomorphological research are identified the roles of organisms in environmental reconstruction trace fossil analysis extraterrestrial geomorphology environmental engineering and the built environment some key research directions and methodological challenges for future biogeomorphological research include expanding the spatial and temporal coverage of datasets investigating the role of bioprocesses in landform development tackling scale issues investigating the relevance of nonlinear dynamical ideas to biogeomorphology and developing better sampling and monitoring techniques for bioprocesses

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

evolution of the navua valles region implications for mars paleoclimatic history abstract the navua valles are comprised of a system of channels and valleys on the inner northeastern rim of hellas basin which is a 1500 km long sloping terrain drainage systems and regional geology in this unique setting were not previously mapped in detail we mapped this region using ctx 6 m px as the base map and assessed surface unit ages resulting from our crater counting we found that the timing of the deposit forming episodes in this region during the hesperian and early to middle amazonian largely correlated to active phases of the hadriacus mons volcanic center we found evidence for several episodes of fluvial activity hesperian to the amazonian with declining intensity and transitioning to ice dominated processes the channels in the navua valles region erode into deposits dating from the noachian to early amazonian including the noachian highlands noachian to early amazonian crater ejecta and likely volcanic plains formed from the hesperian to the hesperian amazonian transition channels directly originating from hadriacus mons are younger while precipitation fed channels at larger distance from the volcanic center are older indicating different triggers for fluvial activity crater counting results indicate that almost all channel floors were at least partially resurfaced during the amazonian and that several channel deposits formed during the last 0 5 gyr water pathways likely included surface channels lakes and subsurface flow the navua valles channel system is discontinuous and the number of terminal deposits sink locations is almost as high as the number of channel sources which is unusual for valley networks elsewhere on mars interior channels formed only in the major navua channels they are even more fragmented than their parent channels but occur along their entire length channels and valley systems within the navua valles are potential targets for in situ astrobiological studies as they could have provided potential habitats at least periodically from the late hesperian to the late amazonian

chaotic obliquity and the nature of the martian climate recent calculations of the martian obliquity suggest that it varies chaotically on timescales longer than about 107 years and varies between about 0 and 60 we examine the seasonal water behavior at obliquities between 40 and 60 up to several tens of centimeters of water may sublime from the polar caps each year and possibly move to the equator where it is more stable co2 frost and co2 h2o clathrate hydrate are stable in the polar deposits below a few tens of meters depth so that the polar cap could contain a significant co2 reservoir if co2 is present it could be left over from the early history of mars also it could be released into the atmosphere during periods of high obliquity causing occasional periods of more clement climate

hydraulic modeling of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle we present a steady state hydraulic model of the tributary and the outlet of a martian paleolake located in the memnonia quadrangle between 167 0 0 w and 167 30 0 w longitude and between 9 25 0 s and 9 45 0 s latitude the mars express high resolution stereo camera hrsc digital elevation model h31850000da4 with a spatial resolution of 75 m is used to describe the geometrical features of the hydraulic system a steady state hydraulic model through a monte carlo procedure is adopted to investigate the assumption that the tributary lake outlet hydraulic system was acting simultaneously during its last water related evolutionary phase through our analysis we infer the roughness coefficient and the discharge of both the tributary and the outlet channels geomorphic evidence such as river terraces were used to constrain the water discharge and the manning s roughness coefficient thereby obtaining estimates of the water level in the lake during the last evolutionary phase of the system our analysis of the outlet reveals a median paleodischarge of 7135 m3 s 1 and a median manning s roughness coefficient of 0 067 m 1 3 s tributary analysis provides a median flow and a median roughness coefficient of 6405 m3 s 1 and 0 123 m 1 3 s respectively moreover the hydraulic analysis suggests that the paleolake water surface level was 1397 m median value hrsc elevation which is consistent with the observed paleoshoreline the results imply that the tributary the lake and the outlet were hydraulically synchronized therefore confirming the presence of a connected water system this study demonstrates that hydraulic analysis can provide valuable information regarding ancient martian water fluxes

searching for evidence of hydrothermal activity at apollinaris mons mars a multidisciplinary approach involving various remote sensing instruments is used to investigate apollinaris mons a prominent volcano on mars as well as the surrounding plains for signs of prolonged hydrologic and volcanic and possibly hydrothermal activity the main findings include 1 evidence from laser altimetry indicating the large thickness 1 5 2 km at some locations of the fan deposits draping the southern flank contrary to previous estimates coupled with possible layering which point to a significant emplacement phase at apollinaris mons 2 corroboration of robinson et al robinson m s mouginis mark p j zimbelman j r wu s s c ablin k k howington kraus a e 1993 icarus 104 301 323 hypothesis regarding the formation of incised valleys on the western flanks by density current erosion which would indicate magma water interaction or alternatively volatile rich magmas early in the volcano s history 3 mounds of diverse geometric shapes many of which display summit depressions and occur among faults and fractures possibly marking venting 4 strong indicators on the flanks of the volcano for lahar events and possibly a caldera lake 5 ubiquitous presence of impact craters displaying fluidized ejecta in both shield forming flank and caldera materials and materials that surround the volcano that are indicative of water rich target materials at the time of impact 6 long term complex association in time among shield forming materials and medusae fossae formation the findings point to a site of extensive volcanic and hydrologic activity with possibly a period of magma water interaction and hydrothermal activity finally we propose that the mound structures around apollinaris should be prime targets for further in situ exploration and search for possible exobiological signatures

orographic precipitation in valley network headwaters constraints on the ancient martian atmosphere 1 we examine the martian valley networks in the framework of topographic influences on precipitation we use an analytical model and the laboratoire de meteorologie dynamique lmd early mars global circulation model gcm to explore the local scale distribution of orographically forced precipitation as a function of atmospheric pressure in simulations with 500 mbar and 1 bar co2 atmospheres orographic lifting results in enhanced snowfall upslope of the observed valley network tributaries our framework also suggests that a 2 bar atmosphere cannot create the observed valley pattern at the highest relief valley network warrego valles as in previous work the gcm does not generate temperatures warm enough for rain or significant snowmelt in the highlands with co2 greenhouse warming alone thus while transient periods of unusual warming are still required to melt the deposits and carve the valleys our model predicts snow deposition in the correct locations

valley formation on early mars by subglacial and fluvial erosion the southern highlands of mars are dissected by hundreds of valley networks which are evidence that water once sculpted the surface characterizing the mechanisms of valley incision may constrain early mars climate and the search for ancient life previous interpretations of the geological record require precipitation and surface water runoff to form the valley networks in contradiction with climate simulations that predict a cold icy ancient mars here we present a global comparative study of valley network morphometry using a principal component based analysis with physical models of fluvial groundwater sapping and glacial and subglacial erosion we found that valley formation involved all these processes but that subglacial and fluvial erosion are the predominant mechanisms this is supported by predictions from models of steady state erosion and geomorphological comparisons to terrestrial analogues the inference of subglacial channels among the valley networks supports the presence of ice sheets that covered the southern highlands during the time of valley network emplacement some valleys in the southern highlands of mars may have formed by subglacial erosion consistent with a cold and icy early mars according to a statistical analysis of valley morphometry

topographic influences on development of martian valley networks 1 some morphometric differences between terrestrial and martian valley networks may reflect the precursor topography on mars particularly impact basins or tectonic slopes to evaluate these possible influences we mapped highland watersheds in nine study areas that sample a range of geographic and topographic settings we collected data including latitude longitude watershed length divide and terminal elevations watershed relief and slope slope orientation and qualitative descriptors including whether a drainage basin was open or closed the longest valley networks and most overflowed basins occur on preexisting intercrater slopes of 0 1 1 particularly on north facing slopes associated with the crustal dichotomy the control of watershed length by earlier noachian topographic features which the relict networks did not significantly modify suggests that the early to middle noachian geomorphic environment was nominally much drier than the later noachian to hesperian transition the distribution of fluvial valleys and likely orographic effects created by the crustal dichotomy suggest that evaporation from the northern lowlands was an important source of atmospheric humidity over short time scales much of the highland plateau consists of smaller enclosed watersheds which along with cooler temperatures detained surface water at high elevations lengthening or impeding the global water cycle ponding and evaporation may have partly offset a continentality effect of the highland landmass prolonged modification of the intercrater geomorphic surface prior to incision of valley networks included substantial weathering reduction of relief and gravity driven sediment transport indicating a long term role for surface water in a transport limited arid to hyperarid noachian paleoclimate

topography of small martian valleys abstract small valleys are common in the ancient highlands of mars valley widths are typically a few kilometers and are independent of length for valleys longer than about 50 km topographic profiles across several representative small valleys produced using one dimensional photoclinometry have smoothly curved shapes and valley side slopes of 10 20 profiles of unusual valleys from maumee valles the flanks of alba patera and softened terrain also have slopes of 10 20 but the profiles of maumee valles are more v shaped than those of the typical small valleys while the profiles of the softened valley have proportionately longer upslope convexities depths from 15 to 800 m are measured for the small martian valleys and most valleys have depths between 20 and 250 m the mean depth to width ratio from 135 measurements of 45 different valleys is 0 08 standard deviation 0 04 when valley profiles with uneven rims are excluded the mean depth to width ratio is 0 07 standard deviation 0 03 applying the lower ratio to the widths of a larger sample of small valleys yields depths that are almost all between 40 and 300 m the majority of the small valleys we have studied are probably the result of groundwater sapping and in this context the measured valley depths imply that liquid water was often less than a few hundred meters below the surface in the vicinity of these valleys at the time early in martian history when the valleys formed

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

assessing the formation of valley networks on a cold early mars predictions for erosion rates and channel morphology abstract the ancient noachian highlands of mars host an extensive population of valley networks which formed predominantly during the early geologic history of the planet morphologic characteristics of the valley networks have been interpreted to indicate the formation of these features through precipitation derived fluvial activity and therefore as evidence for a relatively warm and wet noachian mars climate however these interpretations conflict with the results of sophisticated global climate modeling studies which suggest that early mars was dominated by a cold and icy climate with conditions characterized by adiabatic cooling and regional ice sheets within the highlands difficulties in replicating the warm and wet early climate conditions interpreted from the valley networks has served as the basis for alternative suggestions for the formation of valley networks by transient heating and snowmelt in an otherwise cold and icy climate here we test a conceptual model for valley network formation and incision under cold and icy conditions with a substrate characterized by the presence of an ice free desiccated surface regolith and subjacent ice cemented regolith similar to that found in the antarctic mcmurdo dry valleys on earth we implement numerical thermal models quantitative erosion and transport estimates and morphometric analyses in order to outline and test predictions for 1 the nature and structure of the cold and icy noachian substrate 2 valley network fluvial erosion and incision rates and 3 resulting channel valley morphology morphologic predictions are compared against observational data to determine if the valley networks characteristics are consistent with formation in a cold and icy climate through this approach we present and develop the underlying conceptual model identify and generate the fundamental data inputs required to evaluate it and perform a preliminary first order assessment to serve as a basis for further investigation while these analyses have been performed over a broad parameter space to address relative uncertainties we report findings with a specific emphasis on the nominal results we find that under cold conditions the substrate is characterized by a kilometers thick globally continuous cryosphere with a 50 100 m thick ice free surface layer in diffusive equilibrium with the atmosphere and underlying ice cemented regolith the top of which forms the ice table estimates of the potential infiltration capacity of the ice free surface regolith layer indicate that surface runoff generation does not require excessively large precipitation rates and thus does not preclude fluvial activity sourced by rainfall additionally due to the predicted thicknesses of the ice free surface regolith any transient period of warming would need to be sustained in duration 2 kyr to induce melting of ground ice to initiate solifluction gelifluction activity the predicted range of ice table depths is exceeded by the incised depths of a majority of the valley network population therefore suggesting interactions were possible evaluation of the rates of mechanical substrate erosion and thermal ice cement erosion by valley network fluvial activity are subject to large uncertainties due to several poorly constrained parameters i e the substrate erodibility factor and the valley network fluvial water temperature but generally indicate that at low water temperatures consistent with a cold and icy surface environment thermal erosion of the ice cement can be outpaced by mechanical erosion of the substrate in this scenario the relative efficiency of lateral erosion is predicted to be enhanced during incision below the ice table causing preferential channel valley widening and increased width to depth ratios assessment of this prediction through a morphometric analysis of valley network width to depth ratios and occurrence of u shaped cross sections indicates no significant correlation to ice table depths this result suggests that either 1 permafrost was not present in the noachian mars substrate indicating a warmer climate 2 the permafrost ice table did not significantly influence valley network width to depth ratios possibly owing to more rapid thermal erosion rates than mechanical or 3 additional factors not accounted for in this analysis are involved potential additional factors which could influence the results of this analysis include variable surface geothermal heat flux substrate thermal conductivity substrate composition and physical state as well as valley network preservation state and morphometric sampling biases due to data availability constraints these factors represent areas for future investigation to refine assessments of valley network formation under cold early mars conditions

depth profiles of venusian sinuous rilles and valley networks abstract more than 200 venusian channels and valleys have been mapped based on analyses of magellan sar images sinuous rilles are the most abundant channels among six types of venusian channels and they are widely distributed on venus morphological characteristics of venusian sinuous rilles include sinuous narrowing reaches source depressions and length of several 10s to a few 100s of km this type of channels is known to exist on the moon and possibly on mars valley networks on venus often occur in the vicinity of or in connection to sinuous rilles cross sectional morphologies of sinuous rilles and valley networks are of special importance in discussing their formation processes both qualitatively and quantitatively we reconstructed cross sectional profiles of 6 sinuous rilles and 2 valley networks using a new radar clinometric method reconstructed cross sections revealed that floors of the channels and valleys are clearly lower than the surrounding plains this finding implies that the sinuous rilles and the valley networks have erosional origins longitudinal depth profiles of the sinuous rilles show distinct decreasing trends toward the termini such decreasing trends of depths are qualitatively in agreement with theoretical models and laboratory experiments of thermal erosion in order to verify this assertion quantitatively we conduct simple 1 dimensional model calculations under the assumption that both channel forming lavas and ground substrate are tholeiitic basalt for initial lava thicknesses in the range 2 6 m the model calculations yield good matches to the depth profiles estimated duration of lava effusion ranges from several months to a few years these numerical results support thermal erosion of the sinuous rilles but do not necessarily exclude contributions from mechanical erosion processes valley networks seem to have formed under a strong structural control in comparison to sinuous rilles the valleys vary widely in characteristics of the depth profile and flow directions relative to surface slopes therefore valley networks appear to have originated from diverse formation mechanisms

characterization of fluvial activity in parana valles using different age dating techniques martian valley networks provide the best evidence that the climate on mars was different in the past although these features are located primarily in heavily cratered terrain of noachian age 3 7 ga the ages of the features and the time when they were active is not well understood from superposed craters several recent global studies determined that most valley networks formed during the late noachian to early hesperian however there were some disparities between the techniques in this study our principal objective was to test the reliability of the different age dating techniques to better understand their accuracy and limitations we applied these techniques to parana valles using a variety of high resolution images taken from different instruments that allow us to identify smaller craters d 125 m while providing sufficient coverage to support a statistically reliable sampling of crater populations which is necessary to reduce the uncertainties in age determination our results indicate that parana valles formed during the early hesperian period but that the crater density d 353 m is heterogeneous inside the parana valles basin the crater population decreases from the headwaters downstream recording a resurfacing event that is most likely related to the erosion of downstream sub basins the terrain near the source area is late noachian to early hesperian in age while terrains closer to the outlet are early to late hesperian in age crater densities d 125 m inside the valley are also heterogeneous and record several resurfacing events on the valley floor where the width of the valley network narrows to 2 km we found evidence of an amazonian age eolian deposit that is a relatively thin layer of only few meters that was probably deposited as a result of topographic influences our results validate the reliability of several proposed age dating techniques but we also determined the accuracy and applicability of these techniques our results also demonstrate that crater populations can be used to not only determine the relative ages of valley networks but also to map the distribution of sedimentary materials and the extent of resurfacing events that occurred after valley network formation

interior channels in martian valley networks discharge and runoff production the highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on mars 3 5 ga however determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data new orbital imaging reveals 21 late stage channels within valley networks which we use to estimate formative discharges and to evaluate water supply mechanisms we find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief for 15 narrow channels in basin filling networks likely episodic runoff production rates up to centimeters per day and first order formative discharges of 300 3000 m 3 s are similar to terrestrial floods supplied by precipitation geothermal melting of ground ice would produce discharges 100 times smaller per unit area and would require pulsed outbursts to form the channels in four large valleys with few tributaries wider channels may represent large subsurface outflows or paleolake overflows as these four channels originate at breached basin divides and or near source regions for the catastrophic outflow channels

the origin of fluvial valleys and early geologic history aeolis quadrangle mars in southern aeolis quadrangle in eastern mars parallel slope valleys flat floored branching valleys v shaped branching valleys and flat floored straight canyons dissect the heavily cratered plateau sequence associated knife like ridges are interpreted as fissure eruption vents and thin dark stratiform outcrops are interpreted as exhumed igneous sills or lava flows ridged lava plains are also common but are not themselves modified by fluvial processes i mapped 56 asymmetric scarps or ridges that are probable thrust faults these faults exhibit an orientation vector mean of n63 w 11 95 confidence interval and they transect the lava plains and the older plateau sequence units by comparison the vector mean for the 264 valleys mapped is n48 w 12 with a larger dispersion about the mean the similar orientations displayed by thrust fault and valley axes suggest that valley locations are partly controlled by preexisting thrust faults and related fracture systems most valleys are also arranged orthogonally to and along the perimeter of the ridged plains a possible model for valley development is 1 freshly outgassed water became entombed as frost snow and ice within the cratered terrains during heavy bombardment and the accompanying deposition of impact ejecta volcanic ash and eolian materials 2 effusive volcanism and lava sill emplacement heated subsurface ice in the vicinity of the ridged plains and faults and fractures provided zones of increased permeability for water transport to the surface and 3 headward sapping at thermal springs thermokarst subsidence and limited downvalley fluid flows then carved and modified the valleys

fluidization and hydrothermal alteration of the suevite deposit at the ries crater west germany and implications for mars the formation cooling and alteration of the impact ejecta deposits at the ries crater are an analog for impact processes and the formation of regoliths and soils on mars we have studied the suevite deposit an impact melt bearing breccia found outside of the crater rim this suevite contains large numbers of chimney like degassing pipes apparently formed by high gas pressures in the hot 500 c fluidized suevite immediately after deposition of the suevite the likely sources of the gas are volatiles from the melted and shocked basement inclusions the suevite outside of the crater rim contains about 15 wt clay indicating a large amount of alteration of the suevite the clay is an fe rich montmorillonite with less than 5 interstratified illite indicating that the temperature at which most of the alteration occurred was less than 100 130 c the duration of this low temperature period may have been extended by additional heating from the exothermal alteration reactions the surfaces of the degassing pipes are not altered to clays however but have a thin fe rich oxide or hydroxide coating the absence of alteration in the pipes suggests that the main alteration event outside the crater occurred under unsaturated conditions such that the walls of the pipes were dry suevite deposits are likely to exist on mars because of the presence of volatile rich target rock martian suevites may have also been fluidized and hydrothermally altered contributing significantly to the formation of the clay like phases inferred to exist in the martian soil

plausibility of the white mars hypothesis based upon the thermal nature of the martian subsurface 1 the white mars hypothesis asserts that co2 gas driven debris flows were responsible for carving the outflow channels the valley networks and the gullies on mars rather than liquid water this model further asserts that liquid water has been confined to the deep subsurface unable to find egress to erode the surface we show that the subsurface of mars especially when major fluvial features formed is unlikely to have been as cold as this model suggests and that liquid water would be present much closer to the surface than predicted by white mars the assumptions of the white mars hypothesis regarding globally averaged crustal heat flow are below most estimates of the current thermal state of the martian crust and well below probable values 2 gyr or more ago likewise the assumed value of crustal thermal conductivity in white mars is inconsistent with the co2 dominated cryosphere of the model

amazonian modification of moreux crater record of recent and episodic glaciation in the protonilus mensae region of mars abstract morphologic characteristics of ice rich landforms in the martian mid latitudes record evidence for significant modification of the landscape in response to spin axis orbital parameter driven shifts in the late amazonian climate these landforms are spatially distributed across the mid latitudes and their co existing presence has so far not been observed from a single crater to infer how exactly a terrain has been modified while mars was undergoing major moderate minor shifts in its late amazonian climate we have therefore carried out an in depth investigation of moreux crater 135 km centered at 41 66 n 44 44 e in the protonilus mensae region for identification of features associated with recent and episodic glacial events and for emphasizing the role played by these glacial events in the modification of the crater evidence for extensive modification of the surfaces over crater rim wall and around central peak by emplacement of multiple scales of ice rich landforms that represents large history of glacial activities was found from our results we document phases of major moderate minor glacial activities within the crater as 1 piedmont lobes lobate debris aprons linear valley fills 1 ga 100 ma 2 viscous flow features 30 0 1 ma and 3 gullies thermal contraction crack polygons 2 1 0 4 ma the form and distribution of the random valleys observed within moreux suggests their formation by pressure induced melting and flow occurring beneath an extensive layer of ice we also suggest that central peak of moreux probably acted as the locus for accumulation of ice snow and the diversity of glacial periglacial features within the crater was possibly controlled by differences in the amount of accumulated ice snow and the rate at which the terrain responded to the shifts in climate during subsequent periods of obliquity changes taken together these ice rich deposits within moreux suggest that sequential modification of the crater surfaces over the rim wall and around central peak has occurred over the last tens of millions of years of martian history this new evidence thus adds another well documented case to rapidly accumulating evidences for widespread glacial activity in the middle latitudes of mars in recent martian history

polygenic eruptions on alba patera mars a combination of photogeologic mapping analysis of viking orbiter thermal inertia data and numerical modelling of eruption conditions has permitted us to construct a new model for the evolution of the martian volcano alba patera numerous digitate channel networks on the flanks of the volcano are interpreted to be carved by sapping due to the release of non juvenile water from unconsolidated flank deposits using the thermal inertia measurements we estimate the particle size of these deposits to be 3 10 m which together with theoretical modelling of the disperison of explosively derived volcanic materials leads us to conclude that the flank deposits on alba patera are low relief pyroclastic flows the recognition of numerous late stage summit and sub terminal lava flows thus makes alba patera a unique martian volcano that is transitional between the older pyroclastic dominated highland paterae and the more recent effusive central vent volcanoes such as the tharsis montes

geomorphic study of fluvial landforms on the northern valles marineris plateau mars 1 fluvial landforms are observed on the plateau near echus chasma and other locations on the valles marineris plateau using high resolution 10 to 50 m pixel mars express images and topography branching valleys have a 20 to 100 m deep v shape profile typical of fluvial processes their incision occurred in a thin 150 m and weak dark unit that overlies the plateau basement the valleys are distributed close to watershed boundaries as expected for overland flows and different from pure glacial or hydrothermal processes the 2d geometry of valley networks show drainage densities reaching 1 3 km 1 that indicate a strong 2d extension stage that usually requires a minimum of thousands of years as established from terrestrial examples however the 3d valley geometry shows a limited incision and a lack of concavity suggesting a limited development in time millions of years of evolution are unlikely many outlets connect to the heads of canyons of echus chasma that might involve sapping processes these canyons might have formed coevally with shallow valleys their difference in geometry is a consequence of the difference in lithology which induced a difference in the erosion capacity and an enhanced infiltration conducing to sapping valleys are submitted to modification by aeolian processes sometimes leading to the formation of inverted channels as observed more broadly through the region these landforms formed late in the early mars history and might be considered as examples of episodic fluvial events due to short term climate changes and or regional fluvial activity after the noachian

geomorphology of ma adim vallis mars and associated paleolake basins 1 ma adim vallis one of the largest valleys in the martian highlands appears to have originated by catastrophic overflow of a large paleolake located south of the valley heads ma adim vallis debouched to gusev crater 900 km to the north the landing site for the spirit mars exploration rover support for the paleolake overflow hypothesis comes from the following characteristics 1 with a channel width of 3 km at its head ma adim vallis originates at two eastern and western gaps incised into the divide of the 1 1 m km2 enclosed eridania head basin which suggests a lake as the water source 2 the sinuous course of ma adim vallis is consistent with overland flow controlled by preexisting surface topography and structural control is not evident or required to explain the valley course 3 the nearly constant 5 km width of the inner channel through crater rim breaches the anastomosing course of the wide western tributary the migration of the inner channel to the outer margins of bends in the valley s lower reach a medial sedimentary bar 200 m in height and a step pool sequence are consistent with modeled flows of 1 5 106 m3 s peak discharges were likely higher but are poorly constrained by the relict channel geometry 4 small direct tributary valleys to ma adim vallis have convex up longitudinal profiles suggesting a hanging relationship to a valley that was incised quickly relative to the timescales of tributary development 5 the eridania basin had adequate volume between the initial divide and the incised gap elevations to carve ma adim vallis during a single flood 6 the eridania basin is composed of many overlapping highly degraded and deeply buried impact craters the floor materials of the six largest craters have an unusually high internal relief 1 km and slope 0 5 1 5 among degraded martian craters which are usually flat floored long term fluvial sediment transport appears to have been inhibited within these craters and the topography is inconsistent with basaltic infilling 7 fluvial valleys do not dissect the slopes of these deeper crater floor depressions unlike similar slopes that are dissected at higher levels in the watershed these characteristics 6 7 suggest that water mantled at least the lower parts of the eridania basin floor throughout the period of relatively intense erosion early in martian history the lake level increased and an overflow occurred near the close of the noachian age determined using 5 km crater counts initially the eridania basin debouched northward at two locations into the intermediate basin a highly degraded impact crater 500 km in diameter as this intermediate basin was temporarily filled with water erosion took place first along the lower northern reach of ma adim vallis debouching to gusev crater the western overflow point was later abandoned and erosion of the intermediate basin interior was concentrated along the eastern pathway subsequent air fall deposition impact gardening tectonism and limited fluvial erosion modified the eridania basin region so evidence for a paleolake is restricted to larger landforms that could survive post noachian degradation processes

morphometric analysis of martian valley network basins using a circularity function 1 this paper employs a circularity function to quantify the internal morphology of martian watershed basins in margaritifer sinus region and to infer the primary erosional processes that led to their current geomorphologic characteristics and possible climatic conditions under which these processes operated the circularity function describes the elongation of a watershed basin at different elevations we have used the circularity functions of terrestrial basins that were interpreted as having been modified by 1 erosion related to primarily groundwater sapping and 2 erosion related to primarily rainfall and surface run off as well as the circularity functions of cratering basins on the moon in order to formulate discriminant functions that are able to separate the three types of landforms the spatial pattern of the classification of martian basins based on discriminant functions shows that basins that look morphologically similar to terrestrial fluvial basins are mostly clustered near the mainstream at low elevation while those that look morphologically similar to terrestrial basins interpreted as groundwater sapping origin are located near the tributaries and at higher elevation there are more of the latter than the former this spatial distribution is inconsistent with a continuous earth like warm and wet climate for early mars instead it is more aligned with an overall early dry climate punctuated with episodic wet periods alternatively the concentrated erosion in the mainstream could also be caused by a change of water source from rainfall to snowfall or erosion cut through a duricrust layer

did martian valley networks substantially modify the landscape abstract valley networks are ancient drainage systems incised on the southern hemisphere of mars and stand as evidence that liquid water once sculpted its surface the duration of valley network activity and the sources of water are key questions in deciphering the timing of water stability on early mars but remain poorly constrained in this study we address two questions did martian valley networks evolve for sufficiently long to establish their own erosional basins or do their profiles primarily reflect landscape pre incision topography and were these valleys precipitation fed or spring fed our analysis uses the theoretical framework built to describe the shape of steady state river profiles on earth to compare and analyze the concavity of 62 valley network longitudinal profiles on mars using non linear fits to valley profiles we evaluate the degree to which valley networks are consistent with fluvial steady state the fit enables the identification of valley network concavity index and area discharge exponent which we then interpret in terms of the theoretical framework to discuss valley network maturity and water source our results show that the majority of valley networks do not have concave or even smooth profiles and did not substantially modify their surrounding landscape we observe disparity in concavity indexes of valley networks belonging in the same integrated basins indicating different stages of landscape evolution and lack of synchronous valley development however our results identify six valley networks consistent with fluvial steady state and areally uniform precipitation

mars a review and synthesis of general environments and geological settings of magma h2o interactions the advent of a global cryosphere likely occurred very early in the history of mars and much of the available water and related volatiles co 2 clathrates etc were sequestered within and below the cryosphere this means that magmatism plutonism and volcanism as a geological process throughout the history of mars cannot be fully understood without accounting for the interaction of magma and water and related species in both solid and liquid form we review and outline the probable configuration of water and ice deposits in the history of mars describe environments and modes of magma h 2o interaction and provide specific examples from the geological record of mars magma and water ice interactions have been interpreted to have formed 1 massive pyroclastic deposits 2 large scale ground collapse and chaotic terrain 3 major outflow channels 4 mega lahars dwarfing terrestrial examples 5 sub ice sheet eruptions and edifices 6 pseudocraters 7 landslides on volcanic edifice flanks and 8 hydrothermal sites the global nature of the cryosphere its longevity and the diversity of environments means that mars is an excellent laboratory for the study of magma h 2o interactions and the role of related volatile species

roaming zones of precipitation on ancient mars as recorded in valley networks 1 the 10 largest valley networks in the terra sabaea arabia terra and meridiani planum regions of mars were mapped crater age dated and analyzed by geomorphology stream order and drainage density to understand changes in fluvial erosion during early martian history all of these networks demonstrate characteristics consistent with formation by precipitation many appear to be in different stages of preservation with both highly eroded and pristine valleys sometimes appearing in the same network in some cases the valley network morphologies and crater age dating indicate multiple periods of formation the results from this research place precipitation driven formation of the martian valley networks in terra sabaea arabia terra and meridiani planum in the late noachian and early hesperian epochs 3 6 3 8 billion years ago our age estimates do not extend into earlier or later martian history and the spread in these ages indicates they did not all form or cease formation at the same time the difference in age between the oldest and youngest valley networks in terra sabaea arabia terra and meridiani planum analyzed in this work is 210 50 ma within this range are valley networks that have distinctly separate ages and those that appear to be coeval this research suggests the late noachian and early hesperian were characterized by roaming zones of precipitation that occurred during either continuously warmer and thicker atmospheric conditions or intermittently clement conditions with precipitation occasionally returning to previously rainy regions and overall continuing near meridiani planum longer than in terra sabaea

the western qaidam basin as a potential martian environmental analogue an overview the early martian environment is interpreted as warmer and wetter before a significant change in its global climatic conditions irreversibly led to the current hyper arid environments this transition is one of the most intriguing processes of martian history the extreme climatic change is preserved in the salt deposits desiccated landscapes and geomorphological structures that were shaped by the evaporation of water however until a manned journey to mars is feasible many martian materials morphological structures and much of its evolutionary history will continue to be poorly understood in this regard searching and investigating martian analogues is still meaningful to find an earth environment with a whole set of martian structures distributed at a scale comparable to mars is even more important to test landing crafts and provide optimized working parameters for rovers the western qaidam basin in north tibetan plateau is such a martian analogue the area harbors one of the most extreme hyper arid environments on earth and contains a series of ancient lakes that evaporated at different evolutionary stages during the rise of the tibetan plateau large quantities of salts and geomorphological features formed during the transition of warmer and wet to colder and dry conditions provide unique references to study the modern martian surface and interpret the orbital data we present numerous similarities and results of investigations that suggest the qaidam basin as a potential analogue to study modern geomorphic processes on mars and suggest that this is an essential site to test future mars sample return missions

rheological constraints on martian landslides we use a dynamic finite difference model to simulate martian landslides in the valles marineris canyon system and olympus mons aureole using three different modal rheologies frictional bingham and power law the frictional and bingham modes are applied individually fluidized rheology is treated as a combination of frictional and power law modes general fluidization can include pore pressure contributions whereas acoustic fluidization does not we find that general fluidization most often produces slides that best match landslide geometry in the valles marineris this implies that some amount of supporting liquid or gas was present in the material during failure the profile of the olympus mons aureole is not well matched by any landslide model suggesting an alternative genesis in contrast acoustic fluidization produces the best match for a lunar slide a result anticipated for dry crust with no overlying atmosphere the presence of pressurized fluid during valles marineris landsliding may be due to liquid water beneath a thin cryosphere 1 2 km or flash sublimation of co2

topography of valley networks on mars from mars express high resolution stereo camera digital elevation models 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands the geometry of valley networks can be studied using mars orbiter laser altimeter mola altimetry which is sufficient to map large valleys without a detailed 3 d shape of valley networks imaging from the mars express high resolution stereo camera hrsc is used to generate digital elevation models dems with resolution 50 m and vertical accuracy 60 m we studied valleys near huygens crater and in the aeolis region both in the noachian bedrock and on the west echus plateau in hesperian bedrock hrsc dems in these areas show that 1 drainage density is 3 times higher than is observed in mola data 2 degree of ramification is 1 order more than with mola 3 transverse valley profiles show a v shape more accurately and a minimum depth of 20 m and 4 higher drainage density shows greater headward extension that is not correlated to greater valley depth the deepest valleys 400 m are found in the huygens region where the density in the dem is 0 1 km 1 compared to shallow valleys 100 m of the echus region where the density is higher 0 3 km 1 these regional differences are due to spatially variable preservation and bedrock lithology longitudinal profiles suggest variations in duration of activity profile concavity is only developed in some noachian terrains valleys visible in hrsc images correspond to topographic features in dems showing the same geometry as terrestrial valleys thought to be formed by overland flows and seepage

fluvial response to precipitation variations since 36 ka in the hunshandake sandy land in north china abstract the hunshandake sandy land which is highly sensitive to climate change is located in north china along the margins of the area influenced by the east asian monsoon the upper reach of the xilamulun river which drains the hunshandake sandy land provides an opportunity to test the response of a river landform within a sandy region to climate change we investigated terraces at 4 sites along a 38 km long stretch and performed osl dating on 26 terraces the dating results revealed 23 terraces with unsaturated ages ranging from 0 3 ka to 36 2 ka the observed relationship between the terrace heights and ages is abnormal i e the terrace age does not increase with the terrace height in this case aeolian and fluvial interactions were analyzed and a precipitation dominated terrace formation model was developed higher terraces formed when the riverbed aggraded due to decreased sediment discharge and increased aeolian sand input during a period of reduced precipitation in contrast lower terraces developed when the riverbed eroded during a period of enhanced precipitation we conclude that the terraces along this hunshandake sandy land river respond to precipitation changes even in the absence of background uplift

fresh shallow valleys in the martian midlatitudes as features formed by meltwater flow beneath ice significant numbers of valleys have been identified in the martian midlatitudes 30 60 n s spatially associated with extant or recent ice accumulations many of these valleys date to the amazonian but their formation during these cold dry epochs is problematic in this study we look in detail at the form distribution and quantitative geomorphology of two suites of these valleys and their associated landforms in order to better constrain the processes of their formation since the valleys themselves are so young and thus well preserved uniquely we can constrain valley widths and courses and link these to the topography from the mars orbiter laser altimeter and high resolution stereo camera data we show that the valleys are both qualitatively and quantitatively very similar despite their being 5000 km apart in different hemispheres and around 7 km apart in elevation buffered crater counting indicates that the ages of these networks are statistically identical probably forming during the late amazonian 100 ma in both localities at least tens of valleys cross local drainage divides apparently flowing uphill we interpret these uphill reaches to be characteristic of flow occurring beneath a now absent relatively thin order 101 102 m regionally extensive ice cover ridges and mounds occasionally found at the foot of these valley systems are analogous to eskers and aufeis like refreezing features on the basis of their interaction with these aufeis like mounds we suggest that this suite of landforms may have formed in a single short episode perhaps order of days probably forced by global climate change

glacial landscape and paleoglaciation in terra sabaea evidence for a 3 6 ga polythermal plateau ice cap abstract in a previous study we demonstrated with a comparative morphometrical analysis the first morphometric evidence of a glacial landscape composed of glacial cirques and glacial valleys in the south of terra sabaea at an elevation 1000 m in two impact craters and one mountain the purpose of this study is to use the same method to seek other geomorphologic evidence of glacial landscapes elsewhere in terra sabaea based on a comparison between current and old glacial landscapes on earth and mars we identified 81 glacial valleys and possible evidence for a former plateau ice cap dated at 3 6 ga at the highest elevation in terra sabaea the identified glacial valleys have the same morphometric properties as terrestrial and martian glacial valleys with u shaped cross sectional profiles a v index 0 2 a length to with ratio 1 and a cross sectional area to drainage area ratio four times higher than the fluvial ones moreover these properties are different from terrestrial and martian fluvial valleys we did not find well preserved glacial cirques in this area this absence questions the origin of glacial valleys however the presence of an extensive flat plateau from which the long valleys radiate could have hosted an ancient plateau ice cap which was the source of these glacial valleys a comparison with the cantal and the shaluli shan in the southeastern tibetan plateau on earth reveals morphometrical similarities with our study area in fact long glacial valleys originating radially from a plateau at higher elevation are characteristics of an ancient plateau ice cap this analysis allowed us to propose a polythermal regime for martian glacial landscape namely a cold based ice cap except at the margin where the regime is warmed based due to the steeper topography this topography created shear stress which increased the heat at the base of the ice and created the outlet glacial valleys near the plateau the radial valleys are u shaped with a v index 0 2 but downstream to the low elevation area these valleys become more v shaped with a v index around 0 1 this hypothesis is supported by the presence of an open basin paleolake making the transition between inlet glacial valleys upstream and an outlet v shaped valley downstream so the morphometry of the radiating valleys suggests that liquid water played a role in the formation of this landscape

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

scaling relations for large martian valleys 1 the dendritic morphology of martian valley networks particularly in the noachian highlands has long been argued to imply a warmer wetter early martian climate but the character and extent of this period remains controversial we analyzed scaling relations for the 10 large valley systems incised in terrain of various ages resolvable using the mars orbiter laser altimeter mola and the thermal emission imaging system themis four of the valleys originate in point sources with negligible contributions from tributaries three are very poorly dissected with a few large tributaries separated by long uninterrupted trunks and three exhibit the dendritic branching morphology typical of terrestrial channel networks we generated width area and slope area relationships for each because these relations are identified as either theoretically predicted or robust terrestrial empiricisms for graded precipitation fed perennial channels we also generated distance area relationships hack s law because they similarly represent robust characteristics of terrestrial channels whether perennial or ephemeral we find that the studied martian valleys even the dendritic ones do not satisfy those empiricisms on mars the width area scaling exponent b of 0 7 4 7 contrasts with values of 0 3 0 6 typical of terrestrial channels the slope area scaling exponent ranges from 25 6 5 5 whereas values of 0 3 0 5 are typical on earth the length area or hack s exponent n ranges from 0 47 to 19 2 while values of 0 5 0 6 are found on earth none of the valleys analyzed satisfy all three relations typical of terrestrial perennial channels as such our analysis supports the hypotheses that ephemeral and or immature channel morphologies provide the closest terrestrial analogs to the dendritic networks on mars and point source discharges provide terrestrial analogs best suited to describe the other large martian valleys

discontinuous drainage systems formed by highland precipitation and ground water outflow in the navua valles and southwest hadriacus mons regions mars abstract the navua valles are systems of paleodrainages located north of dao vallis which empty into hellas planitia the largest impact basin on mars in this study we mapped and characterized the navua valles region s individual drainage systems including drainages along the southwestern flank of hadriacus mons and one valley network from the same source as navua valles but flowing in the opposite direction the major drainage systems share morphological characteristics common to both outflow channels and valley networks the slopes in this region are dissected by two major navua drainage systems here navua a and b and several shorter sub parallel valleys formed on the highest gradient approximately 20 m km 1 15 slopes at the lowest part of hellas basin s rim the two major drainage systems originate in the highlands and empty into the basin our mapping suggests that water in navua valles reached the basin floor in a complicated descent and included several episodes of surface ponding surface runoff infiltration subsurface flow and subsequent outflow the most prominent channel system navua a forms a repetitive sequence of deep incision into bedrock followed by a transition into broad channels in erodible materials and then into unconfined deposits this successive erosion transport deposition sequence continues to repeat along the valley s entire length forming a discontinuous pattern that is consistent with classical fluvial process models the channels cut into volcanic plains likely emplaced from the formation of tyrrhenus and hadriacus montes the dendritic source valleys of navua a originate from the rim of a highland crater while the rest of this subsystem consists of a single discontinuous channel which is consistent with a single water source zone that likely supplied water for all channels downslope these drainages may have formed as discontinuous channels revealing the potential existence of subsurface drainage pathways located within an approximately 1 5 10 5 km 2 area water transported underground emerged in segments that are either isolated or aligned downslope from each other we have identified several causes of discontinuities located the zones of potential ground water discharge and recharge and a site of localized precipitation at the headwaters of navua a

experimental delta formation in crater lakes and implications for interpretation of martian deltas 1 the morphology of delta deposits in crater lakes on mars is indicative of upstream e g flow discharge and sediment properties and downstream e g basin characteristics parameters from which the hydrological conditions at the time of formation can be inferred to investigate the influences of these parameters on delta morphology we experimentally created deltas in crater shaped basins by feeding a range of constant flow discharges over a feeder channel of various sand textures we reproduced three categorically different types of deltas including most of the types that have been identified on mars our most striking observation is that water level behavior itself a unique function of flow discharge basin size and hypsometry and basin floor permeability can explain most delta morphologies observed on mars stepped retrograding deltas formed during water level rise prograding deltas formed during water level still stand and during water level fall deltas were partially destroyed by erosion on mars numerous retrograding and prograding deltas were preserved most of them without indications of channel incisions or other fluvial modification we conclude that the main difference between a single foreset prograding delta and a multiple foreset retrograding delta is the behavior of the water level in the basin these simple delta morphologies cannot be reconciled with long duration hydrological activity because that would imply crater lake fluctuations due to inherent complex water level histories along with complex sediment delivery histories our experiments and numerical verifications demonstrate that such deltas preferentially form during one aqueous event which parsimoniously argues for short duration hydrological activity

the structure and evolution of ancient impact basins on mars the number of martian impact basins once thought deficient owing to a low number of impactors has been significantly increased through the identification of structural imprints that remain even after nearly complete erasure of basin massifs five ancient multiringed impact basins were selected for detailed study and exhibit a systematic pattern of rejuvenation of the multiring plan through endogenic modification concentric zones of unstable terrain are believed to reflect deep seated impact related fractures that have localized regional igneous processes in a manner analogous with the basin controlled distribution of basalts on the moon most martian outflow channels were found to originate along the unstable ring zones hydrothermal melting and temporary confinement of channel source materials at sites analogous to lunar sinuous rille source regions are proposed to play an important role in the distribution of martian outflow channels ancient basins also can be delineated by the concentric pattern of topographically and structurally controlled narrow valley networks that are particularly abundant along the outer rings where basin ejecta deposits occur remnant massifs and scarps commonly exhibit extensive furrowing by narrow valley networks perhaps due to a different paleoclimate or sapping during a period of geothermal melting of trapped ices the systematic patterns of valley networks stable and unstable annuli scarps and massifs provide bases for interpreting impact structure in general and for recognizing multiringed structures elsewhere the chryse basin in particular is proposed to represent a major multiringed structure that controlled the formation and distribution of eastern valles marineris and the chaotic terrains of margaritifer sinus in response to volcanism tectonism related to tharsis we conclude that 1 mars is probably not deficient in large body impactors 2 the multiring patterns of basins represent deep seated fracture zones that can be reexposed through subsequent volcanism hydrothermal activity sapping and differential erosion 3 many martian terrains and features e g chaotic terrains and outflow channels are controlled by ancient basins and 4 the resurrection and destruction of impact basins reveal an important third dimension depth for interpreting impact basin formation

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

ancient melting of mid latitude snowpacks on mars as a water source for gullies abstract we hypothesize that during past epochs of high obliquity seasonal snowfields at mid latitudes melted to produce springtime sediment rich surface flows resulting in gully formation significant seasonal mid latitude snowfall does not occur on mars today general circulation model gcm results however suggest that under past climate conditions there may have been centimeters of seasonal mid latitude snowfall mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 gully locations have been tabulated by several researchers e g heldmann j l mellon m t 2004 icarus 168 285 304 heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 malin m c edgett k s 2000 science 288 2330 2335 and found to correspond to mid latitude bands a natural question is whether the latitudinal bands where the gullies are located correspond to areas where the ancient snowfalls may have melted producing runoff which may have incised gullies in this study we model thin snowpacks with thicknesses similar to those predicted by mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 we model these snowpacks under past climate regimes in order to determine whether snowmelt runoff could have occurred and whether significant amounts of warm soil t 273 k existed on both poleward and equatorward slopes in the regions where gullies exist both warm soil and water amounts are modeled because soil and water may have mixed to form a sediment rich flow we begin by applying the snowpack model of williams et al williams k e toon o b heldmann j e mellon m 2008 icarus 196 565 577 to past climate regimes characterized by obliquities of 35 600 ka before present and 45 5 5 ma before present and to all latitudes between 70 n and 70 s we find that the regions containing significant snowmelt runoff correspond to the regions identified by heldmann and mellon heldmann j l mellon m t 2004 icarus 168 285 304 heldmann et al heldmann j l carlsson e johansson h mellon m t toon o b 2007 icarus 188 324 344 and malin and edgett malin m c edgett k s 2000 science 288 2330 2335 as containing large numbers of gullies we find that the snowmelt runoff 1 mm with equivalent rainfall rates of 0 25 mm h and warm soil 1 cm depth would have occurred on slopes within the gullied latitudinal bands the snowfall amounts modeled are predicted to be seasonal mischna m a richardson m i wilson r j mccleese d j 2003 j geophys res planets 108 doi 10 1029 2003je002051 5062 and our modeling finds that under the previous climate regimes there would have been meltwater present on the slopes in question for brief periods of time on the order of days each year our model provides a simple explanation for the latitudinal distribution of the gullies and also suggests that the gullies date to times when water migrated away from the present poles to the mid latitudes

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

correlation between graben orientation channel direction change and tectonic loading the elysium province mars we have investigated the links between regional stress fields the volcanic centers rifts graben and channels in the nw region of the elysium province fig 1 a and fig 1 b to determine whether the sequence of stress events occurring during province development can be derived from the morphologies of these features and thus provide a sequence of development events which is independent of surface dating techniques rift and graben geomorphology was mapped and the neighboring relationships and orientation of individual graben were assessed to determine any spatial clustering or preferred orientation with regional or surface features capable of creating lithospheric flexure or tectonic stress within the study area crosscutting analysis determined a time ordered sequence of graben formation and these were related to volcanic centers or regional sources of stress in addition mapping showed that different channels share sections with similar shape and orientation prompting our study of whether these channels in tandem with the graben were tectonically influenced during their development the channel central axes were mapped and compared to identify common sequences of channel direction change the time sequence of channel direction changes and the time ordered sequence of graben development were then compared we have demonstrated a correlation between rift and graben direction with channel orientation suggesting a regional stress control from evolving volcanic centers overall we derive for the first time the temporal pattern of tectonic volcanic and channel evolution for the northwestern region of this major magmatic province on mars

a new terrestrial analogue site for mars research the qaidam basin tibetan plateau nw china abstract remote sensing observations and rover missions have documented the presence of playas salts and wind erosion landforms of lacustrine sediments on mars all of these observations suggest mars was aqueous in its early history however abundant questions remain how wet was the environment what were the properties of the liquids and the possibility of ancient habitability and what kinds of geological processes shaped the present landforms to explore these unknowns analogue studies can play a key role in this contribution we introduce the qaidam basin tibetan plateau northwestern china as a new and unique analogue site for studying the past aqueous and present arid environments of mars the qaidam basin the highest and one of the largest and driest deserts on earth is located in a dry cold and high uv environment similar to the surface of mars we demonstrate a variety of landforms and also their counterparts on mars which include aeolian dunes and yardangs polygons gullies valleys and fluvial fans in the qaidam basin various environmental regimes for the formation of linear and asymmetric barchans have been described saline lakes and playas representing different stages of lake evolution in arid environment are also present in the qaidam basin and provide promising cases for studying the habitability in mars like environments results for microorganism isolation suggest that halophiles are the most important fraction in the hypersaline sediments and this may shed light on studying present martian habitability moreover the remote but ready accessibility of the qaidam basin make it a potential site for engineering testing in regards to future martin exploration missions we propose that the variety of exogenic and endogenic geomorphic types lacustrine sediments evaporite mineral assemblages and mars like extreme environments collectively point to the qaidam basin as an optimal

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

effects of obliquity and water vapor trace gas greenhouses in the early martian climate 1 we explore possible mechanisms for the generation of warm wet climates on early mars as a result of greenhouse warming by both water vapor and periodic volcanic trace emissions the presence of both water vapor a strong greenhouse gas and other trace greenhouse gases such as so2 in a predominantly co2 atmosphere may act under certain conditions to elevate surface temperatures above the freezing point of liquid water at least episodically variations in obliquity are explored to investigate whether these periodic variations in insolation at mars can broaden the regions or seasons where warm temperatures can exist we use the mars weather research and forecasting general circulation model to perform several simulations of the conditions of the early martian atmosphere containing these gases and find global temperatures to be cooler than the elevated levels suggested by at least one recent study by johnson et al 2008 while achieving temperatures above 273 k globally remains challenging the additional warming by greenhouse gases under certain obliquity states can permit for widespread seasonally warm conditions which can help to explain the presence of fluvial surface features e g valley networks and hydrous minerals of post noachian age a period when alternate methods do not convincingly explain the sustainability of liquid water furthermore we find that global warming can be achieved with the presence of a darker surface globally which is consistent with both widespread exposure of unweathered basaltic bedrock or the presence of a large surface ocean or sea

potential desiccation cracks on mars a synthesis from modeling analogue field studies and global observations potential desiccation polygons pdps are polygonal surface patterns that are a common feature in noachian to hesperian aged phyllosilicate and chloride bearing terrains and have been observed with size scales that range from cm wide by current rovers to 10s of meters wide the global distribution of pdps shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes they are mostly associated with sedimentary deposits that display spectral evidence for the presence of fe mg smectites al rich smectites or less commonly kaolinites carbonates and sulfates in addition pdps may indicate paleolacustrine environments which are of high interest for planetary exploration and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water a collective synthesis with new data particularly from the hirise camera suggests that desiccation cracks may be more common on the surface of mars than previously thought a review of terrestrial research on desiccation processes with emphasis on the theoretical background field studies and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on mars

tharsis tholus an unusual martian volcano tharsis tholus is unusual martian shield volcano in that the edifice is cut by a series of large normal faults that appear to penetrate the entire volcano northeast trending narrow graben also cut the flank the large normal faults may be caused by loading of a ductile subsurface layer allowing failure of the edifice the narrow graben are typical tensional faults the flank is heavily mantled by aeolian material despite the bulbous appearance the overall morphology of tharsis tholus suggests it is a basaltic shield crater counts indicate an age of early hesperian placing tharsis tholus in the middle of the period of activity that built the other small tharsis volcanoes

morphological and morphometric analysis of a topographic depression near huygens basin mars identification of a putative endorheic playa abstract inter crater depressions on mars which may be host to candidate lakes have not been explored in much detail even if a small percentage of these depressions were actually filled with water it would mean that mars was hydrologically more active than previously thought the present study examined valley networks within the equatorial region of mars analysis of the drainage networks around huygens crater revealed a topographically flat basin towards it north the basin was divided into two geological units on the basis of their morphological differences several features including wrinkled ridges dike different types of polygonal desiccation patterns pdps and craters with layered ejecta blankets were observed within the two units estimation of lobateness ejecta mobility and depth to diameter ratio of craters within these units suggest climate controlled fluctuations of volatiles and multiple episodes of resurfacing geological history of the basin was reconstituted and a possible stratigraphy was formulated after integrating basin morphology with cumulative size frequency distribution csfd analysis from the study we infer the basin to be an ephemeral endorheic playa that underwent several geodynamic processes and is a geologically rich terrain for future exploration missions

mineralogic evidence for subglacial volcanism in the sisyphi montes region of mars abstract here we examine the mineral assemblages detected on possible glaciovolcanic edifices in the sisyphi planum region of mars a high latitude region in the southern highlands nestled between the argyre and hellas impact basins minerals were identified utilizing visible near infrared spectra from the compact reconnaissance imaging spectrometer for mars crism analysis of eleven crism images located on the volcanic edifices revealed three distinct spectral classes in the region which are interpreted to be gypsum dominated smectite zeolite iron oxide dominated possibly palagonite and polyhydrated sulfate dominated material while sulfates can form under a variety of alteration conditions palagonite like mineral assemblages require low temperature and high water to rock hydrothermal conditions typically found in subglacial or subaqueous volcanic eruptions the possible palagonite detections on the volcanic edifices the geomorphology of the region and the analogous terrestrial mineralogy of subglacial eruptions strongly suggests the formation of these minerals during subglacial eruptions or associated hydrothermal systems this implies that thick water ice sheets were present in this region in the late noachian or early hesperian and that the subglacial hydrothermal systems could have supported habitable environments with excellent biosignature preservation potential

volcanic geology of hadriaca patera and the eastern hellas region of mars hadriaca patera is a low relief volcano in the southern highlands of mars northeast of the hellas basin layered friable deposits composing the extensive channeled flanks of the volcano surround a well defined summit caldera containing late stage eruptive products the morphologic characteristics of the channels suggest erosion by groundwater sapping and surface runoff the erosional morphology of the volcano the lack of lava flow features and the friable nature of the flank materials indicate that hadriaca patera consists predominantly of pyroclastic deposits gravity driven flow models demonstrate that the distribution of flank materials can be attributed to the emplacement of pyroclastic flows both magmatic and hydromagmatic eruption models are viable for the magmatic case the necessary mass eruption rates 107 108 kg s ejection velocities 400 m s and volatile contents 1 5 3 0 wt h2o are consistent with parameters derived for terrestrial plinian eruptions for the hydromagmatic case the required energy conversion efficiencies are comparable to those of laboratory experiments and the inferred permeability of the martian crust allows large amounts of groundwater to be transported rapidly at flow rates of 103 104 m3 s into the region models of cooling during emplacement indicate that welding of pyroclastic flows can occur at large distances hundreds of kilometers from a source vent on mars the layering within hadriaca patera could be attributed to welding of pyroclastic flows that would control its susceptibility to erosion morphologic similarities between hadriaca and tyrrhena paterae suggest a similar volcanic history with an early pyroclastic dominated shield building phase followed by effusive eruptions at their summit calderas and on the flank of tyrrhena patera the formation of the extensive ridged plains of hesperia planum following the formation of the highland paterae supports the interpretation of a transition from explosive to effusive volcanism in the eastern hellas region a progressive depletion of volatiles on mars is consistent with the morphologic properties of highland paterae and other central vent volcanoes a predominance of hydrovolcanic eruptions in the development of hadriaca and tyrrhena paterae would imply that the transition in volcanic eruption style can be attributed to a volatile depletion of the crust whereas magmatic eruptions at the paterae would be indicative of temporal changes in martian magmas

mars reconnaissance orbiter observations of light toned layered deposits and associated fluvial landforms on the plateaus adjacent to valles marineris abstract we have used data from the mars reconnaissance orbiter to study 30 80 m thick light toned layered deposits on the plateaus adjacent to valles marineris at five locations 1 south of ius chasma 2 south of western melas chasma 3 south of western candor chasma 4 west of juventae chasma and 5 west of ganges chasma the beds within these deposits have unique variations in brightness color mineralogy and erosional properties that are not typically observed in light toned layered deposits within valles marineris or many other equatorial areas on mars reflectance spectra indicate these deposits contain opaline silica and fe sulfates consistent with low temperature acidic aqueous alteration of basaltic materials we have found valley or channel systems associated with the layered deposits at all five locations and the volcanic plains adjacent to juventae ius and ganges exhibit inverted channels composed of light toned beds valleys channels and light toned layering along the walls of juventae and melas chasmata are most likely coeval to the aqueous activity that affected the adjacent plateaus and indicate some hydrological activity occurred after formation of the chasmata although the source of water and sediment remains uncertain the strong correlation between fluvial landforms and light toned layered deposits argues for sustained precipitation surface runoff and fluvial deposition occurring during the hesperian on the plateaus adjacent to valles marineris and along portions of chasmata walls

explosive volcanism on hecates tholus mars investigation of eruption conditions evidence is presented supporting the identification of a discrete well preserved air fall deposit generated by explosive volcanism on mars the deposit is located immediately to the west of the summit caldera of hecates tholus 32on 209ow the northernmost of the three volcanic constructs in the elysium planitia region the absence of superposed impact craters larger than the resolution limit of the viking images 40 m per pixel indicates a very young age for this eruption which evidently postdates even the most recent collapse episode of the olympus mons caldera 300 m y b p neukum and hiller 1981 from the distribution of craters smaller than 2 km in diameter it appears that the air fall material mantles an area about 50 x 75 km in extent to an estimated thickness of about 100 m by adapting numerical models for terrestrial volcanic eruptions to the martian environment these dimensions imply an eruption cloud height of about 70 km in order to attain such an altitude the mass eruption rate must have been 107 kg s and the volatile content either 1 wt for h20 or 2 wt for co2 although it is not possible to distinguish between silicic and basaltic volcanism on hecates were the volatile species co2 the depth of most recent storage prior to eruption of the magma would have to be 50 100 km due to the solubility of co2 in the melt if h20 were the driving volatile a minimum depth of storage would be 0 2 4 km thereby permitting the possibility of ground water assimilation by the magma

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

assessment of environmental controls on acid sulfate alteration at active volcanoes in nicaragua applications to relic hydrothermal systems on mars 1 a variety of secondary mineralogies has been detected on mars from both orbiters and landers indicating widespread aqueous alteration of the crust many of these locales exhibit sulfates which in some cases imply acidic fluids at present there are few constraints on the paleoenvironmental conditions that existed during formation of the widespread and diverse classes of secondary minerals on mars we investigated hydrothermal systems at three active acidic volcanic systems in nicaragua including cerro negro momotombo and telica the recently erupted materials are similar in composition to the martian crust and are undergoing extensive acid sulfate alteration predominately in gas dominated settings fumaroles we characterized the secondary mineralogy and local variables including temperature ph rock and gas composition and fluid rock ratio we find that these environmental parameters exhibit strong controls on the alteration mineralogy the environments studied include ph that ranged from 1 to 6 temperatures from ambient to hundreds of degrees celsius and fumaroles to hot springs the hottest and most acidic systems contained sulfur silica and minor gypsum while moderately acidic and cooler fumaroles included abundant silica gypsum and other hydrated sulfates and phyllosilicates a setting with a higher fluid rock ratio but similar temperature and acidity was dominated by phyllosilicates and to a lesser degree sulfates the characterization of aqueous alteration of basalts under a variety of environmental conditions provides a conceptual framework for interpretation of similar relic environments on mars finally while identification of phyllosilicates on mars is generally thought to require neutral to alkaline fluids we documented significant formation of these minerals in the acidic volcanic systems

hypsometric analysis of margaritifer sinus and origin of valley networks 1 the formation of martian valley networks has been debated since their discovery the relative roles of groundwater sapping and fluvial runoff processes have different implications on martian paleoclimate this paper uses a hypsometric analysis technique that has been tested on terrestrial landforms to analyze the hypsometric attributes of watershed basins in the margaritifer sinus region on mars using mars orbiter laser altimeter mola gridded topographic data on the basis of quantitative characteristics of their hypsometric attributes the majority of the basins covering 3 5 of the study area look more like terrestrial basins of sapping origin and a significant number of basins covering 1 5 of the study area are more fluvial like the classification of the rest of the basin is less certain at the presently available resolution of the digital elevation model dem overlay with viking photomosaic indicates that the classification is generally consistent with the morphology shown in viking images although this analysis alone cannot make a sure determination of valley network origin combined with other morphometric analysis the results from this study are consistent with a valley network formation by precipitation recharged groundwater sapping suggesting a warm and wet climate for early mars

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

periodic instabilities during compression or extension of the lithosphere 1 deformation modes from an analytical perturbation method we argue that the plastic rheology of the lithosphere rather than its recoverable elastic properties is responsible for the systematic development of periodic instabilities during compression or extension we use a linear perturbation model with analytical solutions to calculate the instability modes for various rheologies the growth of such periodic instabilities is enhanced by the highly nonlinear stress strain rheologies encountered in the brittle layers of the lithosphere on the contrary ductile layers deforming according to high temperature creep flow laws tend to inhibit these instabilities for oceanic domains we assume that the only brittle layer is the upper part of the lithosphere in compression the only valid instability is a buckling whose wavelength is around 4 times the thickness of the brittle layer calculated wavelengths and growth rates are consistent with observations available for the indian ocean for continental domains a reasonable assumption is the existence of two plastic layers one in the upper crust the other in the upper mantle for moho temperatures between 450 c and 600 c in compression and extension two instabilities develop a long wavelength instability involving the whole lithosphere coupling mode and a short wavelength instability involving the crust and controlled by the upper brittle layer intrinsic crustal mode in compression the coupling mode is a whole lithosphere buckling with a wavelength about 4 times the thickness of the active lithosphere the two plastic layers plus the intermediate ductile layer in extension the coupling mode is a boudinage of opposite phase in the two plastic layers and a folding of the intermediate ductile layer the intrinsic crustal mode is a crustal buckling in compression crustal boudinage in extension neither deflects the moho the intrinsic crustal mode is favored by an increase in thermal gradient and by a decrease in strength of the ductile lower crust

ancient glaciation on mars a large number of anomalous landforms on mars can be attributed to glaciation including the action of ice and meltwater glacial landscapes are concentrated south of lat 33 and in the northern plains suggesting vast austral and boreal ice sheets crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in martian history thus mars may have had a relatively warm moist climate and dense atmosphere much later than previously believed

structural setting and timing of hydrothermal veins and breccias on hurd peninsula south shetland islands a possible volcanic related epithermal system in deformed turbidites quartz veins and vein breccias in a greywacke shale sequence of carboniferous triassic age were previously regarded as mesothermal silicified fault breccias and related to an adjacent eocene granodiorite pluton new mapping of vein assemblages and textures and their structural and cross cutting relationships demonstrates that the steeply dipping sheeted epithermal textured vein array was hydraulic in origin and possibly cretaceous in age the main vein and breccia swarm trends for 14 km nne along strike and 2 km across strike cutting large irregular areas of silicified and brecciated sandstone and patchy areas of pyritic propylitic and k feldspar alteration angular vein fabrics and hydraulic disruption textures indicate wedging by hydrothermal solutions hydraulic rupture brecciation and fragment transport followed by open space precipitation in veins generally 15 cm thick and breccias up to a few metres thick hydrothermal quartz chlorite calcite and chalcedony predominate with variable amounts of chalcopyrite galena sphalerite and pyrite epidote arsenopyrite k feldspar and andradite garnet are conspicuous in places breccias were pre and syn mineralization whereas mineral precipitation was pre syn and post breccia formation hydrothermal activity was simultaneous with extensional faulting striking nne and accompanied by intrusion of dacitic dykes there followed conjugate shearing on east and ese striking faults intrusion of high level tonalite stocks and several phases of basaltic andesite dyke intrusion these hypabyssal rocks were probably coeval with the antarctic peninsula volcanic group dominating livingston island dated between 130 and 75 ma minor copper and iron sulphide bearing veins occur in adjacent volcanic and hypabyssal intrusive rocks the hurd peninsula veins may therefore form part of a volcanic epithermal hydrothermal system adularia sericite quartz type of cretaceous age rather than a porphyry related system of eocene age

drainage network development in the keanakāko i tephra kīlauea volcano hawai i implications for fluvial erosion and valley network formation on early mars 1 a number of studies have attempted to characterize martian valley and channel networks to date however little attention has been paid to the role of lithology which could influence the rate of incision morphology and hydrology as well as the characteristics of transported materials here we present an analysis of the physical and hydrologic characteristics of drainage networks gullies and channels that have incised the keanak ko i tephra a basaltic pyroclastic deposit that occurs mainly in the summit area of k lauea volcano and in the adjoining ka desert hawai i the keanak ko i tephra is up to 10 m meters thick and largely devoid of vegetation making it a good analog for the martian surface although the scales are different the keanak ko i drainage networks suggest that several typical morphologic characteristics of martian valley networks may be controlled by lithology in combination with ephemeral flood characteristics many gully headwalls and knickpoints within the drainage networks are amphitheater shaped which results from strong over weak stratigraphy beds of fine ash commonly bearing accretionary lapilli pisolites are more resistant to erosion than the interbedded coarser weakly consolidated and friable tephra layers because the banks of the gullies and channels are easily eroded widths vary downslope similar to martian valley networks that have been characterized as degraded the floors of the gullies and channels tend to be low relief with few prominent bed forms reflecting the large proportion of sediment transported as bed load in high energy but short lived flood events we calculate that the average flow velocities within the drainage networks are typically 1 m 24 h given some recent modeling of the early martian climate our observations imply that rainfall on early mars could also be associated with large intense events and that martian valley network formation may be related to similar cyclonic storms

volcanic processes as alternative mechanisms of landform development at a candidate crater lake site near tyrrhena patera mars 1 palos crater a prominent candidate crater lake site in the hesperia region of mars is located at the mouth of a sinuous inlet channel that extends from the northern flanks of tyrrhena patera previous studies of this site have concluded that channels and basin infill units likely formed through aqueous processes that partly involved karst like removal of materials in the subsurface by the flow of groundwater as with many locales on mars the aqueous processes hypothesized to have been involved in the formation and evolution of terrain features are compelling however the characteristics of this site suggest that an alternative set of mechanisms for landform development should be considered alongside aqueous hypotheses the main attributes of channels and infill of the central crater include 1 an association with a very large volcanic rise to the south 2 the existence of roofed segments of the main inlet channel and 3 infill of the central crater and outlet channel by materials that have characteristics consistent with those expected of volcanic plains these general attributes are consistent with formation through or in association with processes that involved the flow of lava although a volcanic model may account for the presence and basic nature of landforms previously considered supportive of a paleolake interpretation of the site an overprint of dendritic valley networks on parts of the inlet system suggests that aqueous processes may have also acted in the evolution of the site a complex interrelation between past igneous and aqueous processes at this site is possible

the contributions of biogeomorphology to the emerging field of geobiology biogeomorphology has developed into a well established research field over the past 15 years with studies examining a range of two way interrelations between organisms and geomorphology in a variety of terrestrial and marine environments this paper starts by defining the core biogeomorphological processes bioerosion bioprotection and bioconstruction particular emphasis is placed on the study of bioconstructional forms providing a clear definition examples of bioconstructions and crucially examining important interactions between bioconstruction and bioerosion three key areas where biogeomorphological research can directly contribute to the emerging field of geobiology are identified 1 the use of biogeomorphological approaches combined with palaeoecological investigations and predictive modelling in the growing field of carbon sequestration and climate change mitigation 2 providing geomorphological expertise to support the emerging field of astrobiology and 3 the potential contributions of biogeomorphology to the blossoming field of bio geoengineering some key research directions and challenges for future biogeomorphological research include exploring how biogeomorphological studies can contribute to and benefit from collaborations with other fields of geobiology and assisting in the development of a useful effective interdisciplinary toolbox of methods to improve quantification of geobiological processes importantly suggestions are made for potentially fruitful collaborations with geomicrobiologists geochemists and palaeoecologists

the polygonal surface structures in the dalangtan playa qaidam basin nw china controlling factors for their formation and implications for analogous martian landforms