thickness and extent of the subglacial till layer beneath an antarctic paleo ice stream fast flowing ice streams and outlet glaciers currently account for as much as 90 of the discharge from the antarctic and greenland ice sheets although the deformation of subglacial material has been proposed as the mechanism for this rapid motion such sediment is usually hidden under several kilometers of ice marine geophysical records have allowed reconstruction of the three dimensional thickness of the sedimentary bed beneath a large antarctic paleo ice stream for the first time fast flow is indicated by streamlined seafloor lineations that form the surface of a layer of low shear strength unsorted sediment averaging 4 6 m thick rapid motion of the paleo ice stream was a result of subglacial deformation within this layer

the simud tiu valles hydrologic system a multidisciplinary study of a possible site for future mars on site exploration abstract when looking for traces of past life on mars we have to look primarily for places where water was present possibly for long time intervals the simud and tiu valles are two large outflow channels connected to the north with the chryse basin oxia palus quadrangle the area carved by water during the noachian early hesperian is characterized by a complex geological evolution the geomorphological analysis shows the presence of fluvial and alluvial structures interpreted as fluvial channels and terraces debris flow fronts and short lasting small water flows coexisting with maar diatremes and mud volcanoes several morphological features indicate a change in water flux direction after the main erosive phase during this period water originated from the masursky crater and flown southwards into the hydraotes chaos this phenomenon caused the studied area to become a depocenter where fine grained material deposition took place possibly in association with ponding water this setting is potentially quite valuable as traces of life may have been preserved the presence of water at various times over a period of about 1 ga in the area is corroborated by mineralogical analyses of different areas that indicate the possible presence of hydrated minerals mixtures such as sulfate bearing deposits given the uniqueness of the evolution of this region the long term interactions between fluvial volcanic and tectonic processes and its extremely favorable landing parameters elevation slope roughness rock distribution thermal inertia albedo etc we decided to propose this location as a possible landing site for the esa exomars 2018 the nasa mars 2020 and future on site missions

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

compositional heterogeneity of the ancient martian crust analysis of ares vallis bedrock with themis and tes data 1 themis multispectral and thermophysical information combined with tes hyperspectral and albedo data is used as a powerful high spectral spatial resolution tool to investigate the mineralogic heterogeneity of ancient martian crust exposed in ares vallis bedrock three major spectral units are present in the upper ares vallis region 1 a regional unit that is composed primarily of a high silica si o 0 35 component with lesser amounts of plagioclase and pyroxene and is associated with channel wall rock and surrounding plains 2 a pyroxene and olivine rich rock unit exposed as a 250 m thick contiguous layer in the wall rock of ares vallis as well as in isolated exposures in the plains outside of the channel and 3 a unit composed of plagioclase pyroxene and lesser high silica component s si o 0 35 that primarily occurs as low albedo sand the spatial and stratigraphic distribution of these units suggests that the pyroxene and olivine enriched unit may be extrusive and or intrusive in origin indicating that this region experienced either a single stage or repeated episodes of olivine enriched magmatism during the first 1 5 gyr of crust formation this olivine enrichment may have been caused by a larger degree of mantle partial melting facilitated by higher mantle temperature melting from a more depleted mantle source and or less olivine fractionation relative to regional rock parent magmas the olivine rich unit is similar in thermophysical character to previously published olivine bearing terrains on mars but the derived modal mineralogy consists of 20 more pyroxene and less plagioclase than those terrains

numerical simulations of large scale cataclysmic floodwater a simple depth averaged model and an illustrative application a simple numerical simulation code is developed to quantitatively discuss the behaviors of past cataclysmic floods whose rigorous hydraulic descriptions would be too complex to be supported by typically available field data the code aims to keep the basic equations simple and the required computational costs low which allows greater exploration of parameter space examination of both the qualitative meaning of turbulent equations and the relative importance of terms in the shallow water equation have resulted in the adoption of the depth averaged diffusion wave approximation in two dimensions as well as manning s empirical equation for simplification on the other hand topography is included as a boundary condition since topography plays an important role in selecting flood routes the model provides important advantages over theoretical analyses or one dimensional simulations including 1 the reproduction of complicated water flow paths such as bifurcations and reconvergences 2 the reconstruction of hydrological relationships among the water paths and 3 the direct comparison among the calculated extent of the flood inundation including floodwater depths and geological and geomorphological observations preliminary reconstructions of the missoula floods demonstrate the advantages of this new approach the method of coupling field based flood information with two dimensional analysis of an entire flow path provides a basis for estimating the peak discharges and flow durations of cataclysmic megafloods on earth with direct bearing on the understanding of regional paleohydrological histories of mars

geology of xanthe terra outflow channels and the mars pathfinder landing site the mars pathfinder landing site mpls was selected for its location at the mouths of ares and tiu valles outflow channels on mars where sediments from a variety of geologic units could have accumulated in a lacustrine environment recent geologic mapping at 1 2 m scale of the xanthe terra channels and chryse planitia near mpls reveals a progression of fluvial erosion and deposition throughout the hesperian period from the geology the watersheds of the channels were inferred and a sequence of paleogeologic maps was produced three outflow episodes are recognized 1 broad sheetwash during the early hesperian emanating from eastern valles marineris and equatorial chaos regions with initial erosion into highland plateau basement 2 early channel formation and 3 subsequent flooding which deepened the channels to their current morphologies the most recent flooding issued from simud and tiu valles during the late hesperian indicated by stratigraphic superposition striations along the floor of the channel and the orientation of streamlined islands in the flood direction this suggests that surface sediments deposited at mpls are most likely to have come from these channels and to a lesser extent from ares vallis a ranking scheme was developed to assess the potential origins for the sediments found at mpls the most abundant materials are inferred to have come from the noachian and hesperian highland plains and reworked sediments from previous floods underlying materials from earlier floods could also be found at mpls as ejecta from nearby impact craters

thermokarst landforms and processes in ares vallis mars abstract with a length of 1500 km ares vallis is one of the largest martian outflow channels and is inferred to have been formed by cataclysmic floods of water conveyed from source areas which are marked by chaotic terrain to chryse planitia near its downstream outlet 14 n 28 w the floor of ares widens to 100 km from its average 25 km width this area of widened channel floor is marked by a complex of irregular terraces elongated depressions linear ridges sinuous ridges and other indicators of highly irregular dissection of a formerly continuous surface thermokarst processes following either glacial or alluvial histories seem best to explain these relationships various indicators of fluctuating discharge for water and sediment ponding of debris and prolonged flow suggest the emplacement of ice rich debris in the anomalous reach of ares vallis post flood or post glacial thawing of the ice rich sediments would then generate the thermokarst landscape these processes which are consistent with other indicators of anomalously warm climatic conditions imply a profound change from the modern martian environment

outflow channel sources reactivation and chaos formation xanthe terra mars abstract the undulating warped and densely fractured surfaces of highland regions east of valles marineris located north of the eastern aureum chaos east of the hydraotes chaos and south of the hydaspis chaos resulted from extensional surface warping related to ground subsidence caused when pressurized water confined in subterranean caverns was released to the surface water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of ares tiu and simud valles of the eastern part of the circum chryse outflow channel system progressive surface subsidence and associated reduction of the subsurface cavernous volume and or episodes of magmatic driven activity led to increases of the hydrostatic pressure resulting in reactivation of both catastrophic and non catastrophic outflow activity ancient cratered highland and basin materials that underwent large scale subsidence grade into densely fractured terrains collapse of rock materials in these regions resulted in the formation of chaotic terrains which occur in and near the headwaters of the eastern circum chryse outflow channels the deepest chaotic terrain in the hydaspis chaos region resulted from the collapse of pre existing outflow channel floors the release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow basal warming related to dike intrusions thermokarst activity involving wet sediments and or dissected ice enriched country rock permafrost exposed to the atmosphere by extensional tectonism and channel incision and or the injection of water into porous floor material may have enhanced outflow channel floor instability and subsequent collapse in addition to the possible genetic linkage to outflow channel development dating back to at least the late noachian clear disruption of impact craters with pristine ejecta blankets and rims as well as preservation of fine tectonic fabrics suggest that plateau subsidence and chaos formation may have continued well into the amazonian period the geologic and paleohydrologic histories presented here have important implications as new mechanisms for outflow channel formation and other fluvial activity are described and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation and thus chaotic terrains mark prime locations for future geologic hydrologic and possible astrobiologic exploration

did ice streams carve martian outflow channels outflow channels on mars1 are long sinuous linear depressions that occur mostly in the equatorial area 30 lat they differ from small valley networks2 by being larger and arising full born from chaotic terrains outflow channels resemble terrestrial stream beds and their origin has generally been attributed to water3 5 in catastrophic floods6 7 or mudflows8 the catastrophic flood hypothesis is derived primarily from the morphological similarities of martian outflow channels and features created by the catastrophic spokane flood that formed the washington scablands these similarities have been documented extensively3 6 7 but differences of scale remain a major problem martian channel features are on the average much larger than their proposed terrestrial analogues we examine here the problem of channel origin from the perspective of erosional characteristics and the resultant landf orms created by former and present day ice streams and glaciers on earth from morphologic comparisons an ice stream origin seems equally well suited to explain the occurrences and form of the outflow channels on mars and in contrast with the hydraulic hypothesis ice streams and ice sheets produce terrestrial features of the same scale as those observed on mars

overview of the mars pathfinder mission and assessment of landing site predictions chemical analyses returned by mars pathfinder indicate that some rocks may be high in silica implying differentiated parent materials rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past the moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius composite airborne dust particles appear magnetized by freeze dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle remote sensing data at a scale of generally greater than 1 kilometer and an earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust free

volcanic rilles streamlined islands and the origin of outflow channels on mars 1 the widely accepted view that catastrophic flow of liquid water was the dominant process involved in formation of outflow channels on mars has as part of its foundation the assumption that the flow of lava could not have formed martian features such as streamlined islands and anastamosing channels however lunar and venusian channels believed to have formed through volcanic processes in the absence of water are indeed associated with such features additionally many lunar and venusian rilles head at topographic depressions a common characteristic of martian outflow channels lunar rilles typically lack positive relief accumulations of volcanic deposits at their mouths suggesting that contrary to previous assertions absence of such accumulations at the mouths of martian outflow channels is not incompatible with a common mode of formation consistent with an igneous origin for outflow channels and certain valley systems on mars volcanic processes can produce a wide range of landforms that are similar to those normally associated with the flow of water including channel terraces and complex channel networks the simplest interpretation of martian channels that extend from volcanic source regions onto volcanic plains is as conduits formed by the flow of lava channel formation hypotheses requiring major changes in martian atmospheric properties or repeated catastrophic flow of water from volcanic features appear needlessly exotic alongside the igneous hypothesis for channel formation in light of these points future investigations of martian outflow channels should more actively consider volcanic processes as candidate mechanisms for channel formation

contribution to the study of thermal erosion on mars similar to the coldest terrestrial periglacial regions like yakutia siberia the planet mars exhibits wide outflow channels this analogy and the presence of permanent ground ice suggest that thermal erosion have existed during martian fluvial outbursts 3000 m y ago thermal erosion here is considered to be the result of ground thawing produced by heat transfer between the water flow and the frozen ground followed by a transport of unfrozen sediments this paper proposes a qualitative explanation of thermal erosion with the help of some physical models from the quantitative point of view two thermal mathematical models are proposed and discussed the zones undergoing the most efficient erosion are river banks the first model studied here describes extreme thermomechanical actions a constant thermal flux on the ground surface produces ground thaw and the unfrozen sediments are immediately removed by water flow it is an ablation model it allows a theoretical evaluation of the river bank recession validity of theoretical estimations is acquired by comparing the calculations to the observed backwearing of the banks of some siberian rivers which can reach 25 m yr 1 thermal erosion acting upon the bottom of wide rivers on mars or in siberia as well is a very complex mechanism indeed the mathematical modeling requires the study of interaction between thermal processes and transport of sediments laws these laws are not yet well defined and are very difficult to establish thus another model presented in this paper concerns only one dimensional thermal actions of water flow upon the bottom of wide rivers it considers fluvial flow at positive celsius temperature producing a thermal flux from the bottom to the initially frozen semi infinite ground this model considers a constant convective heat transfer coefficient and allows an estimation of the thickness of the thawed ground beneath the river talik calculated thickness of the melted ground is given in the paper for different periods of time

the geologic history of margaritifer basin mars in this study we investigate the fluvial sedimentary and volcanic history of margaritifer basin and the uzboi ladon morava outflow channel system this network of valleys and basins spans more than 8000 km in length linking the fluvially dissected southern highlands and argyre basin with the northern lowlands via ares vallis compositionally thermophysically and morphologically distinct geologic units are identified and are used to place critical relative stratigraphic constraints on the timing of geologic processes in margaritifer basin our analyses show that fluvial activity was separated in time by significant episodes of geologic activity including the widespread volcanic resurfacing of margaritifer basin and the formation of chaos terrain the most recent fluvial activity within margaritifer basin appears to terminate at a region of chaos terrain suggesting possible communication between surface and subsurface water reservoirs we conclude with a discussion of the implications of these observations on our current knowledge of martian hydrologic evolution in this important region

a refined chronology of catastrophic outflow events in ares vallis mars abstract we investigate the geomorphology and chronology of catastrophic flooding in a major martian outflow channel ares vallis we use recently acquired stereo and colour images and derived topographic data with grid spacing of 50 m from the high resolution stereo camera hrsc onboard mars express to constrain the detailed flood geomorphology of proximal ares vallis we identify morphologic evidence for 6 distinct erosion surfaces that were likely formed by multiple episodes of catastrophic flooding these surfaces occur at distinct topographic levels exhibit multiple sets of flood grooves and contain distinct post flood crater populations crater count statistics on the flood eroded surfaces from mro context camera ctx and thermal emission imaging system themis visible images indicate that flooding was initiated during the late noachian early hesperian at 3 6 ga the morphology data confirm that the oldest flooding events occurred on the topographically highest erosion surfaces while subsequent floods abandoned the upper surfaces and continued to modify craters in the topographically lowest main channel of ares vallis into the late hesperian early amazonian 2 5 ga our results suggest that release of water to ares vallis likely occurred at repeated intervals over a long period of geological time thus supporting recent numerical modelling studies that suggest a recharging water source

ice sculpture in the martian outflow channels many landforms in martian outflow channels have characteristics that suggest sculpture by glaciers ice streams or ice sheets viking orbiter and terrestrial satellite images were examined at similar resolution to compare features of the martian outflow channels to features produced by the movement of ice on earth many resemblances were found they include the anastomoses sinuosities and u shaped cross profiles of valleys hanging valleys and linear scour marks on valley walls grooves and ridges on valley floors and streamlining of bedrock highs the question of whether ice could have moved in the martian environment is investigated since gradients on martian channel floors are extremely low or even reversed a certain thickness of ice is required to initiate glacial motion if ice filled the martian channels to the level of interior plateaus flow could have occurred even under present climatic conditions although warmer climates in the past would have been more favorable additionally if the channel fluids were brines ice might have been wet based and would have moved readily by slipping over the ground it is envisioned that springs or small catastrophic outbursts discharged fluids from structural outlets or chaotic terrains the fluids built icings that may have grown into substantial masses and eventually flowed like glaciers down preexisting valleys alternatively the fluids may have formed rivers or floods that formed ice jams and consolidated into icy masses in places where obstacles blocked their flow these masses of ice or slush were probably episodic and temporary but where they occurred within the channels they may have produced landforms that are characteristic of glacial sculpture on earth

late noachian to hesperian climate change on mars evidence of episodic warming from transient crater lakes near ares vallis 1 the ares vallis region is surrounded by highland terrain containing both degraded and pristine large impact craters that suggest a change in climate during the late noachian early hesperian from warmer wetter conditions to colder dryer conditions however the regional occurrence of hesperian age crater outlet channels indicates that this period on mars was characterized by episodic climate fluctuations that caused transient warming facilitating the stability of liquid water at the surface an extensive survey of the morphology and topography of 75 impact basins in the region indicates that of the largest degraded craters 4 were identified with single outlet channels that suggest the former presence of water infill these basins lack inlets indicating that water influx was likely derived from sapping of groundwater a comparison of measured crater rim heights to modeled rim heights suggests that the bulk of the depth diameter reduction on these craters was the result of infilling possibly by sediments crater statistics indicate that crater degradation and infill occurred during a short 200 ma interval in the late noachian from 3 8 ga to 3 6 ga craters that formed after 3 6 ga exhibit a near pristine morphology our results support the hypothesis of rapid climate change at the end of the noachian period however geologic relationships between the crater outlet channels and ares vallis indicate that drainage occurred only after the period of intense crater modification during the hesperian 3 5 2 9 ga this suggests a delay between the time of infill of the craters and the time of drainage

outwash plains and thermokarst on mars abstract the spatial distribution of different types of rampart craters on mars suggests a hemispheric asymmetry in the distribution of ground ice the northern plains especially major topographic depressions near the terminations of outflow channels have high percentages of rampart craters two of these basins acidalia and utopia planitiae received extraordinarily large amounts of water and sediment from the chryse and elysium outflow channels in both regions the analysis of high resolution viking pictures 12 m pixel indicates a concentration of kilometer scale depressions that are similar in size and form to thermokarstic features in yakutia siberia and parts of the arctic coastal plain of north america accordingly we infer that 1 utopia planitia and acidalia planitia may contain thick laterally continuous ice rich sedimentary deposits related to outflow channel forming floods and 2 these areas of mars may have experienced thermokarstic processes similar to modern thermokarstic processes in some periglacial regions of earth

evidence for persistent flow and aqueous sedimentation on early mars landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in mars global surveyor mars orbiter camera and mars odyssey thermal emission imaging system images evidence of distributary channelized flow in particular flow that lasted long enough to foster meandering and the resulting deposition of a fan shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial and potentially lacustrine environments

propagating solitary waves along a rapidly moving crack front a rapidly moving crack in a brittle material is often idealized1 as a one dimensional object with a singular tip moving through a two dimensional material however in real three dimensional materials tensile cracks form a planar surface whose edge is a rapidly moving one dimensional singular front the dynamics of these fronts under repetitive interaction2 3 4 with material inhomogeneities asperities and the morphology5 6 7 8 9 10 11 of the fracture surface that they create are not yet understood here we show that perturbations12 to a crack front in a brittle material result in long lived and highly localized waves which we call front waves these waves exhibit a unique characteristic shape and propagate along the crack front at approximately13 14 15 the rayleigh wave speed the speed of sound along a free surface following interaction counter propagating front waves retain both their shape and amplitude they create characteristic traces along the fracture surface providing cracks with both inertia and a new mode of dissipation front waves are intrinsically three dimensional and cannot exist in conventional two dimensional theories of fracture1 because front waves can transport and distribute asperity induced energy fluctuations throughout the crack front they may help to explain how cracks remain a single coherent entity despite repeated interactions with randomly dispersed asperities

paleohydrology and flood geomorphology of ares vallis ares vallis is a martian outflow channel which is about 1500 km long and locally exceeds 100 km in width and 1000 m in depth we estimate the channel s paleoflow capacity using paleohydraulic techniques at a constricted and unusually deep reach not affected by tributaries or secondary inflows the estimated possible maximum peak discharges are of the order of 108 109 m3 s these values are 1 to 2 orders of magnitude larger than any known terrestrial floods these high discharge flows were theoretically capable of transporting boulders larger than 10 m in diameter the downstream depositional plain where ares debauches into the chryse planitia displays geomorphological features indicative of high erosional capacity by the flooding in this area site of the proposed pathfinder landing we expect to find a complex sequence of sediments created by varying paleoflood flow hydraulics sediment transport characteristics and probable secondary modification of the primary flood landforms

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

major episodes of geologic history of isidis planitia on mars abstract we have mapped the area of isidis planitia 1 27 n 75 103 e in order to assess the geologic history of this region using modern data sets such as mola topography and the high resolution images provided by the hrsc ctx and hirise cameras results of our mapping show that the geologic history of isidis planitia consists of three principal episodes 1 impact dominated episode noachian until 3 8 ga during this time the oldest materials in the study area were formed mostly by impact reworking and mass wasting other processes e g volcanism and fluvial glacial activity likely operated at this time but played a subordinate role 2 an episode related to volcanic and fluvial glacial activities late noachian early amazonian 3 8 2 8 ga volcanism appears as the most important process at the beginning of this episode 3 8 3 5 ga and was responsible for the formation of a large circum isidis volcanic province by the early hesperian epoch volcanic materials covered large portions of the isidis rim almost completely buried the previous crater record on the floor of the isidis basin and probably were the major contributors to the filling of the basin fluvial glacial processes prevailed closer to the end of the episode early hesperian early amazonian 3 5 2 8 ga and were responsible for widespread resurfacing in the isidis planitia region mostly at 3 1 3 4 ga glaciers and or ice sheets probably resulted in a massive glaciation of the rim and the floor of the isidis basin the total volume of material eroded from the isidis rim by glacial and fluvial activity is estimated to be about 35 000 50 000 km 3 which is equivalent to a composite layer about 40 60 m thick on entire floor of the basin more important however is that the eroded materials were likely saturated with ice water and could form wet deposits on the floor 3 wind dominated episode since early amazonian 2 8 ga wind activity dominated the later geologic history of isidis planitia but resulted only in minor modification of the surface

debris flow origin for the simud tiu deposit on mars a late hesperian smooth plains deposit on mars interpreted as a debris flow extends more than 2000 km from hydraotes chaos through simud and tiu valles and into chryse planitia the simud tiu deposit widens out to 1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity morphologic features of the simud tiu deposit observed in viking and pathfinder images are generally consistent with a debris flow origin but some of the deposit s salient features are not readily explained by catastrophic flooding or ice flow internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow possible flow lobes within the deposit may have formed by successive flow surges within the flow unit the pathfinder landing site is on the simud tiu deposit and the observations there are consistent with debris flow the low longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt imbricated planar rocks on the ridges such as in the rock garden also may have been emplaced by debris or ice flow however stream energy calculations at ares vallis and channel geology indicate that flooding probably was incapable of emplacing the meter size boulders observed at the pathfinder site dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material the debris flow unit apparently coalesced from outflows of water fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of simud and tiu valles the deposit is onlapped from the north by another flow deposit originating from acidalia planitia if the simud tiu debris flow had entered a standing body of water a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the acidalia deposit

deep water erosional remnants in eastern offshore trinidad as terrestrial analogs for teardrop shaped islands on mars implications for outflow channel formation discovery of geomorphological elements such as valleys and channel like features on the surface of mars has prompted debate over alternative origins for these morphologies including erosion by lava liquid co 2 glaciation and mass wasting events similarities between martian geomorphological elements and those of certain terrestrial environments suggest that water processes were involved in the formation of some visible martian landscapes recent advances in three dimensional seismic reflectivity imaging techniques drawn mainly from oil and gas exploration activities in deep water regions of the world have allowed us to describe a variety of internal stratigraphic architectures that resemble some geomorphological features observed in the circum chryse planitia region of mars for example erosional shadow remnants that have been described as components of deep water mass transport deposits in the eastern offshore margin of trinidad closely resemble teardrop shaped islands that have been described at the downstream end of outflow channels within the circum chryse planitia region these observations suggest that the teardrop shaped islands might have been formed as a result of catastrophic submarine mass movements similar to those documented within continental margins on earth

antarctic ice streams and outflow channels on mars new sonar images of the antarctic sea floor reveal mega scale glacial lineations that are strikingly similar to longitudinal flutes in martian outflow channels the analogs suggest that ice moved through the martian channels in places and carved the flutes the ice in martian channels may have moved like antarctic ice streams on deformable debris saturated with water under high pore pressure on mars water at the base of ice filled channels may have come from residual water or melt water liberated during past warmer climates or higher heat flows

an isotopic c o sr study of vein gold deposits in the meguma terrane nova scotia implication for source reservoirs vein quartz carbonate and tourmaline from 19 meguma gold deposits in the meguma terrane of nova scotia have been analyzed for stable delta 18 o delta 13 c and radiogenic 87 sr 86 sr isotopes in order to assess the nature and origin of the vein forming fluids as with other mesothermal gold provinces the meguma gold deposits are well suited to such a study because carbonate is the next most abundant phase after quartz in these mesothermal lode gold deposits all vein types have been sampled for quartz and carbonate and in addition all compositional and textural varieties of carbonate have been sampled vein quartz is of uniform isotopic composition with most 18 o values between 10 2 to 17 6 per mil avg ca 14 per mil except for one deposit west gore sb au where values go to 19 4 per mil there is no systematic variation for quartz within a deposit or position within the meguma group stratigraphy vein carbonate 18 o values range from 11 8 to 27 5 per mil with most in the 13 to 16 per mil range the relatively 18 o enriched carbonates reflect exchange with low temperature fluids based on analyses of quartz carbonate pairs that indicate disequilibrium fractionation delta sub quartz carbonate or 0 this is best illustrated by the strong negative correlation between delta 18 o carbonate and delta sub quartz carbonate the 18 o water is estimated at 10 or 3 per mil for a temperature of vein formation of 350 degrees to 400 degrees c and using the appropriate mineral water fractionation equations whereas delta 18 o water values partly overlap the field for magmatic fluids the values are wholly consistent with a metamorphic fluid and it is considered unlikely that a primary magmatic fluid signature has been substantially modified due to wall rock influences given that mesothermal gold systems are sites of high fluid rock ratios vein carbonate has delta 13 c values of 13 1 to 25 9 per mil but a slight negative correlation between delta 13 c carbonate and delta sub quartz carbonate suggests that the primary values lie in the range 20 to 25 per mil thus the delta 13 c values indicate a reduced biogenic source for the carbon oxidation of the reduced carbon as indicated by co 2 in fluid inclusions may have occurred via hydrolysis of graphite or dissolution of carbonate minerals both of which occur in the wall rock lithologies of the meguma group the latter of which has the appropriate isotopic composition the initial 87 sr 86 sr of the vein fluid estimated from the analyses of 52 vein carbonates 17 deposits and four tourmalines three deposits ranges from 0 70118 to 0 72284 and within deposits considerable variation is observed there is insufficient data to quantify the extent of the low temperature overprint which has modified the c and o isotope data although it is likely that some influence is present nevertheless the data cannot be reconciled by a source confined exclusively to the meguma group which suggests therefore involvement of another reservoir s the isotopic heterogeneity can be explained by variable amounts of contamination of a primary fluid with radiogenic sr derived from meguma group lithologies by interaction along the fluid path or at the site of vein formation concomitant with wall rock alteration as discussed above a dominantly magmatic source is not considered feasible this fluid source is suggested to be within the structural basement to the meguma group and the liscomb gneisses are the favored source based on the combined results of the sr isotope data presented herein and previously published pb isotope data collectively the data indicate that a primary fluid of metamorphic origin has had its isotopic signature variably modified due to interaction with different reservoirs the most affected isotopic systems are c and s based on earlier work on delta 34 s values which are abundant as graphite carbonate and sulfides in the meguma wall rock respectively the range in 87 sr 86 sr values of the fluid also reflects contamination but this was quite variable the uniform delta 18 o water value for the fluid indicates that this was the least affected isotopic system except for the later exchange of carbonate at low temperatures

hydrographs of a martian flood from the breach of galilaei crater abstract spectacular floods were spawned on mars when large craters filled to overtopping and catastrophically breached the wealth of data now available permits quantitative analysis of these ancient floods galilaei crater is examined here along with the likely sources of its water and the processes that formed tana vallis its 1 km deep outflow channel laser altimetry data stereo photogrammetry and scaled images are used to reconstruct the lake volume and the geometry of the preserved breach it is theorized that surface flows from hydaspis chaos eroded the rim and floor of galilaei crater and partly filled the basin leading to degradation of the underlying cryosphere groundwater released from a confined aquifer then slowly filled galilaei crater until the enclosed lake overtopped its rim the resulting flood breached the crater wall rapidly drained the lake and eroded tana vallis the drainable lake volume was 1 110 1013 m3 based on laser altimetry data from mars global surveyor this volume was 90 of the volume in lake superior in the great lakes using the reconstructed breach and channel geometry methods used to analyze terrestrial dam breaches were applied to produce hydrographs of lake stage and discharge peak flood discharge in tana vallis likely ranged from 1 5 to 4 7 107 m3 s 1 mean channel incision rates are estimated at 0 333 0 133 and 0 0667 m min 1 for scenarios in which tana vallis formed in 2 5 and 10 days for the 5 day breach erosion scenario stream power per unit streambed area at the time of peak discharge was estimated at 3 5 105 w m 2 the volume of material eroded to form the vallis was only 3 of the lake volume that drained in 5 days open channel calculations were performed to compare with the dam breach hydrographs for tana vallis the channel as seen today never flowed bank full or even at three fourths its maximum depth because the implied flows would have exceeded peak discharges from the crater breach i also evaluate an alternative model catastrophic ice lake collapse for the morphology and breach of aram chaos a large crater near galilaei crater that model has fundamental difficulties because of improbable assumptions and inadequate consideration of the knowledge base of terrestrial basalt hydrology the model of ice lake collapse fails to explain the breach and outflow of crater lakes like those that existed in aram chaos and galilaei crater the present analysis supports a simpler model of groundwater inflow that fills a crater to overtopping this model harmonizes with the low elevations of aram chaos and galilaei crater and is more consistent with extensive evidence of fluid breakouts in this region and with theoretical and terrestrial knowledge

geological evolution of ares vallis on mars formation by multiple events of catastrophic flooding glacial and periglacial processes abstract ares vallis is one of the greatest outflow channels of mars using high resolution images of recent missions to mars mgs 2001 odyssey and mars express we investigated ares vallis and its valley arms taking advantage of 3 dimensional analysis performed using the high resolution stereo capability of the mars express high resolution stereo camera hrsc in our view ares vallis is characterized by catastrophic flood landscapes partially superimposed by ice related morphologies catastrophic flood landforms include erosional terraces grooved terrains streamlined uplands giant bars pendant bars and cataract like features ice related morphologies include probable kame features thermokarstic depressions and patterned grounds our investigations outline that throughout the hesperian age ares vallis and its valley arms had been sculpted by several time scattered catastrophic floods originating from iani hydaspis and aram chaos geomorphological evidence suggests that catastrophic floods were ice covered and that climatic conditions of mars at this time were similar to those of the present day at the end of each catastrophic flood ice masses grounded forming a thick stagnant dead ice body each catastrophic flood was followed by a relatively brief period of warmer wetter climatic conditions originated as a consequence of catastrophic flooding during such periods thermokarstic depressions originated liquid water formed meandering channels and ice contact deposits were emplaced by ice walled streams finally the climate turned into cold dry conditions similar to the present day ones and ice masses sublimated

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd