observations at the mars pathfinder site do they provide unequivocal evidence of catastrophic flooding after mars pathfinder landed at the mouth of ares valus a large channel that drains into the chryse planitia basin the mission reports unanimously supported the interpretation that the lander site is the locus of catastrophic flooding by noting that all aspects of the scene are consistent with this interpretation however alternatives cannot be ruled out by any site observations as all aspects of the scene are equally consistent with other interpretations of origin namely ice and mass flow processes subsequently modified by wind erosion the authors discuss alternative explanations for the geologic history of the channel based on a regional view of the circum chryse channels from viking images our best broad scale information to date and the local view from the recent pathfinder landing site mega indicators of channel origin the regional geomorphology geology and planetary climatic conditions taken together suggest some combination of flood mass flow glacial and eolian processes the macro indicators of channel origin sedimentologic are also not indicative of one process of emplacement either as single criteria or taken cumulatively finally the micro indicators of channel origin geochemical and mineralogic composition do not provide very tight constraints on the deposits possible origins other than that water was in some way involved

buried topography of utopia mars persistence of a giant impact depression knobs partially buried craters ring fractures and some mesas permit a qualitative determination of the topography buried beneath younger northern plains materials these features are widely distributed in the utopia area but are absent in a large roughly circular region centered at about 48 degree n 240 degree w this implies the existence of a circular depression about 3 300 km in diameter buried beneath utopia planitia that is here interpreted to represent the central part of a very large impact basin the presence of buried curved massifs around part of this depression and a roughly coincident mascon lend further support present topography areal geology and paleotopography of buried surfaces all point to the persistence of this major depression for almost the entire history of mars

deltaic deposits at aeolis dorsa sedimentary evidence for a standing body of water on the northern plains of mars a fundamental long standing question regarding mars history is whether the flat and low lying northern plains ever hosted an ocean the best opportunity to solve this problem is provided by stratigraphic observations of sedimentary deposits onlapping the crustal dichotomy here we use high resolution imagery and topography to analyze a branching network of inverted channel and channel lobe deposits in the aeolis dorsa region just north of the dichotomy boundary observations of stacked cross cutting channel bodies and stratal geometries indicate that these landforms represent exhumed distributary channel deposits observations of depositional trunk feeder channel bodies a lack of evidence for past topographic confinement channel avulsions at similar elevations and the presence of a strong break in dip slope between topset and foreset beds suggest that this distributary system was most likely a delta rather than an alluvial fan or submarine fan sediment transport calculations using both measured and derived channel geometries indicate a minimum delta deposition time on the order of 400 years the location of this delta within a thick and widespread clastic wedge abutting the crustal dichotomy boundary unconfined by any observable craters suggests a standing body of water potentially 105 km2 in extent or greater and is spatially consistent with hypotheses for a northern ocean

north polar region of mars topography of circumpolar deposits from mars orbiter laser altimeter mola data and evidence for asymmetric retreat of the polar cap we have used high resolution mars orbiter laser altimeter mola data to analyze the topography morphology stratigraphy and geologic history of the martian north circumpolar deposits the present polar deposits are offset about toward 0 w from the rotational pole an arc of irregular topography concentric to olympia planitia and the cap consists of polar material remnants depressions which we interpret to be kettles frost covered and residual ice filled craters and frost patches olympia planitia originally thought to be a flat sand covered plain is characterized by a convex upward topography contiguous with the polar cap we interpret olympia planitia to represent a now dune covered extension of the polar materials together olympia planitia and the outlying deposits delineate a former extent of the polar cap topographic data have clarified relationships among the circumpolar deposits contributors to these deposits include local volcanics fluvial and aqueous sediments from outflow channels and a possible standing body of water pyroclastic ash sublimation lag from the olympia lobe and eolian reworked materials significant events in the history of the region include 1 formation of the northern lowlands 2 emplacement of volcanic plains fluvial and aqueous sedimentation and subsequent desiccation forming polygonal patterns which in part underlie the present polar layered deposits 3 formation of the polar cap composed primarily of layered deposits 4 asymmetric retreat of the olympia lobe resulting in sublimation lag deposits polar remnants and kettles and 5 continued collection and reworking of sediments by eolian processes the cause of the asymmetrical retreat of the olympia lobe is unknown

huge co2 charged debris flow deposit and tectonic sagging in the northern plains of mars the northern plains of mars contain a vast deposit covering one sixth of the planet that apparently resulted in extensive lithospheric deformation the center of the deposit may be as much as 2 3 km thick the deposit has lobate margins consistent with the flow of fluidized debris for hundreds to thousands of kilometers derived from highland and high plains sources the deposit surface lowers inward by 900 m in places and is locally bordered by a bulge 300 m high similar deformation accompanied development of pleistocene ice sheets on earth the lack of burial of a large inlier of older terrain and the response time of the mantle to the loading require that the deposit was emplaced in 2 as an active agent in the processes of source rock collapse and debris flow

chasma boreale mars a sapping and outflow channel with a tectono thermal origin abstract a detailed geomorphological study of chasma boreale a widely known feature of mars north polar cap has been carried out for the first time along with a quantitative paleohydrological model it is concluded that the chasma was eroded by a flow whose discharge was on the order of magnitude of 10 9 m sec 1 this catastrophic flow is thought to have been preceded by a powerful sapping process caused by a tectonically focused thermal event several lines of evidence indicate tectonic control in the distribution and present aspect of most of the polar troughs this tectonic forcing probably played a major role in the inception of not only chasma boreale but also other polar reentrants as well

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

the geology of the viking lander 2 site revisited abstract reevaluating the geologic history of the prior mars landing sites provides important ground truth for recent and ongoing orbital missions at the viking 2 lander vl2 site topographic measurements of relict landforms indicate that at least 100 m of sedimentary mantle material has been stripped away the observed paucity of impact craters

transitional morphology in west deuteronilus mensae mars implications for modification of the lowland upland boundary abstract west deuteronilus mensae which lies along the lowland upland boundary of mars at 45 latitude 345 longitude exhibits both gradational l a rossbacher 1985 in models in geomorphology woldenberg ed pp 343 372 allen unwin boston and fretted terrain r p sharp 1973 j geophys res 78 4073 4083 boundary types to the west the boundary is gradational and to the east it is defined by fretted terrain the two types of boundaries do not merge with one another within the west deuteronilus mensae region however the gradational boundary materials appear to overlap the fretted terrain by about 500 km contacts between units associated with the gradational boundary and the fretted terrain boundary can both be recognized in the region of overlap the fretted terrain can be identified as much as 300 km north of the gradational boundary in this region lowland units associated with the gradational boundary embay canyons of the fretted terrain in a topographically conformal fashion changes in the fretted terrain across the gradational boundary from uplands to lowlands include a reduction of canyon wall slopes and depths such that the fretted terrain north of the gradational boundary appears mantled but not obscured there are at least two major classes of processes which might explain the lateral overlap 1 erosion of stratified upland terrain and 2 deposition of plains materials onto the sloping upland margin and fretted terrain erosion of stratified upland terrain does not adequately explain the plainward decrease in crater densities across the gradational boundary nor is it consistent with evidence that lowland plains material appears to onlap the sloping upland margin in several places of the possible plains emplacement mechanisms eolian deposition would not produce the sharp apparently topographically conformal gradational unit contacts volcanics plains emplacement would not preserve the complex geometry of the underlying fretted terrain sediment deposition in either a liquid or ice covered sea could produce the draped appearance of the fretted terrain outflow channels along the lowland upland boundary particularly those of the circum chryse and west elysium regions may have flooded the northern lowlands to depths of tens to hundreds of meters the gradational unit contacts may represent the shorelines of such a sea the scale of characteristic morphologies along these contacts may require an unfrozen condition of sufficient duration to allow lacustrine style wave erosion and redistribution of material along the contacts our limited understanding of the martian paleoclimate and h 2 o inventories allows the possibility of clement periods in the past and other geological evidence e g small valley networks and outflow channels strongly suggests an extensive role of liquid water

oceans in the past history of mars tests for their presence using mars orbiter laser altimeter mola data an ancient north polar ocean on mars has been proposed parker et al 1989 and we use mola data to test the hypothesis of the two proposed contacts shorelines the younger contact 2 shows the closest approximation to an equipotential surface vertical variations along this surface oc cur in areas with post contact formation geological activity or suspected changes in the position of an equipotential surface e g tharsis with time the surface of mars is smoother at all scales below contact 2 than above the volume of the re gion below contact 2 1 5 x 107 km 3 is between the mini mum estimated total outflow channel discharge and the maxi mum estimated megaregolith pore space these results are con sistent with the hypothesis that a large standing body of water occupied the northern lowlands in the past history of mars gin to account for the draped appearance they interpreted the plains to represent sediment deposition in a sea and suggested that the gradational unit contact represents the shoreline in a subsequent more regional analysis parker et al 1993 noted that the northern lowland plains comprise one third of mars surface area that most outflow channels valley networks empty into the lowlands and that channel cutting does not ex tend far into the plains although the regional basinward topo graphic gradient continues into the northern lowlands they raised the question of where the water went and favored the hypothesis that the channels represented streams that flooded the northern lowlands to produce a standing body of water see also lucchitta et al 1986 gulick and baker 1989 baker et

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

possible sub glacial eruptions in the galaxias quadrangle mars we have identified several landforms in the galaxias quadrangle of mars mtm 35217 33 0 35 5 n 216 0 218 0 w which are consistent with this area having been covered by an ancient ice sheet concurrent with volcanic eruptions volcanic activity was initiated by the intrusion of several large dikes measuring 50 100 m wide and protruding up to 35 m above the present day surface these dikes appear to have originated from elysium planitia 600 km to the se in one instance a dike at an elevation of 3750 m appears to have produced a subglacial mound referred to here as galaxias mons 2 that evolved into an extrusive eruption and produced copious volumes of melt water that carved an outflow channel that extends almost 300 km to the north at a lower elevation 3980 m a second putative dike may have failed to break the surface of the ice sheet and formed galaxias mons as a laccolithic intrusion we numerically model the formation of galaxias mons and find that at least 200 m of ice may once have existed at this latitude at the time of the dike intrusions such a conclusion supports the idea that enigmatic small domes in the area may be pingoes collectively these observations suggest that the previous interpretations for the origin of near by hrad vallis as a sub aerial eruption may need to be revised

syrtis major and isidis basin contact morphological and topographic characteristics of syrtis major lava flows and material of the vastitas borealis formation received 18 october 2002 revised 10 march 2003 accepted 14 april 2003 published 28 june 2003 1 the floor of isidis basin is covered by materials of the vastitas borealis formation vbf that appear to be emplaced essentially as a single unit along its western boundary isidis basin is in contact with volcanic flows from syrtis major planum the contact between the isidis unit and volcanic flows from syrtis major is sharp to gradational and in places is characterized by a high 500 m scarp or by a network of faults that separate pieces of lava plains off the main plateau of syrtis clusters of knobs and mesas sometimes arranged in flow like features are also typical features of the transition zone several important characteristics of the transition from syrtis major to isidis basin are documented 1 the small scale surface texture seen in moc images appears to be the same for both the syrtis lava plateau and the knobs and mesas that characterize the transition 2 there is strong evidence for the breakup of the coherent surface of syrtis major where it is in contact with materials in isidis basin 3 the plateau breakup the knobby terrain occurs basinward after the major break of slope of syrtis major where it enters the isidis basin 4 there is no evidence for plateau breakup anywhere up on the slopes of syrtis major planum 5 the lavas of syrtis remain morphologically intact where they are in contact with other units such as the noachian cratered terrain or where lava flows are stacked within syrtis major itself these characteristic features of the transition zone from syrtis to isidis are readily explained if the zone of plateau breakup consists of relatively young lava flows that have been superimposed onto the surface of a volatile rich substratum such as the interior unit of isidis basin the vastitas borealis formation thus simple superposition of volcanic materials on top of volatile bearing sediments can explain the key geological and topographic aspects of the transition zone from syrtis major to isidis basin on the basis of our findings we outline the following scenario for the evolution of this region in the early hesperian volcanic plains are emplaced in syrtis major the lower part of the syrtis major formation and wrinkle ridges deform their surfaces soon thereafter concurrently volcanic plains are emplaced on the floor of the isidis basin and wrinkle ridges deform their surfaces soon thereafter the apparent simultaneity of these units may mean that syrtis major was the source of many of the flows in the isidis basin in the early part of the upper hesperian subsequent to the formation of most of the wrinkle ridges the vastitas borealis formation was emplaced in the isidis basin and elsewhere in the northern lowlands following the emplacement of the vastitas borealis formation the upper part of the syrtis major formation was emplaced erupting from the eastern margins of syrtis major planum and flowing down into the westernmost part of the isidis basin on top of the recently emplaced vastitas borealis formation modification of the superposed lavas by degradation and evolution of the vbf formed the scarps and unusual morphology of the marginal areas we found no compelling evidence for massive or sudden erosion from syrtis major to produce the plains currently on the surface of the floor of the isidis basin the vastitas borealis

oceans on mars an assessment of the observational evidence and possible fate the edges of the northern plains and interpreted to be shorelines remaining from these former standing bodies of water we examine the elevations and geologic relations along these contacts in detail and find little support for their interpretation as shorelines some contacts are clearly of volcanic origin and all have significant variations in elevation better support for the former presence of water over large parts of the northern plains is provided by the vastitas borealis formation vbf most of the post noachian fill within the northern basin is ridged plains of lower hesperian age interpreted to be volcanic in origin overlying the ridged plains is the vbf a thin veneer of material of upper hesperian age the vbf may have been deposited from large floods support for this interpretation is the similarity in age between the outflow channels and the vbf the presence of the vbf at the lower ends of the outflow channels and identification of numerous features in the outcrop areas of the vbf that are suggestive of basal melting of an ice sheet to cover all the area over which the vbf is exposed would require 2 3 10 7 km 3 of water spread over the entire surface of mars this volume is equal to a global layer global equivalent layer or gel 156 m deep we find no support for the larger estimates of ocean volumes that range up to 3 10 8 km 3 and which imply comparable amounts of water per unit area as are currently present on the surface of the earth under present climatic conditions on mars an ocean would freeze in a geologically short time period 10 4 years then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface the present vbf is interpreted as a sublimation residue from the ponded outflow channel effluents the fate of a volume of water thought to have been emplaced by the outflow channels 2 3 10 7 km 3 is largely accounted for by the presence of other existing reservoirs on the planet an approximately 20 30 m gel of water is estimated to be in the present polar caps and a 50 m gel may have escaped to space since the hesperian leaving 80 m gel unaccounted for this amount may be partly trapped in other volatile rich deposits on the surface and a significant amount could have reentered the groundwater system by south polar basal melting and been progressively cold trapped at the base of a growing cryosphere on the basis of our assessment of the hesperian aged deposits we predict that testing of the clifford and parker 2001 hypothesis that a noachian aged ocean covered up to one third of the surface of mars will be made very difficult by the enhanced degradation rates in the noachian and subsequent geological events in the northern lowlands index terms 6225 planetology solar system objects mars 4267 oceanography general paleoceanography 5407 planetary sciences atmospheres evolution 5470 planetary sciences surface materials and properties 1635 global change oceans 4203 keywords mars oceans channels shorelines hesperian

karst on mars the thumbprint terrain abstract some instances of the so called thumbprint terrain of the northern plains of mars may be caused by differential solution of large carbonate deposits occupying low lying areas and may represent an analog to the arid karst of the nullarbor plain in australia based on the comparative morphology of the two regions

chryse basin channels low gradients and ponded flows gradients on the floors of the martian outflow channels that are derived from radar elevation profiles across lunae planum and the chryse basin have much lower values than those obtained from the u s geological survey s topographic map to arrive at this conclusion 26 radar elevation profiles clustered at four latitudinal channel crossings were analyzed and approximate longitudinal gradients of the channel floors were constructed whereas the gradients of maja and ares valles are similar to those of the catastrophic flood channels in the scablands of washington state and water or ice could have moved through them without difficulty the gradients of simud and tiu valles are essentially level and the movement of fluids to the north poses problems it is proposed that ponding from local runoff occurred before channel formation along the course of simud and tiu valles the ponding may have formed lakes in depressions associated with the valles marineris grabens ancient craters in the chaotic terrain area and possibly even the regional low where most chaotic terrains occur it is envisioned that lakes eventually overflowed drainages became integrated and headward erosion breached interfluves thus forming the present channel configurations when dams broke floods mudflows or mixtures of water sediments and ice were released catastrophically with a final gigantic flood from the valles marineris system of troughs this flood would have had sufficient head to move fluids across nearly level gradients through the simud and tiu channels the ponding and flooding probably occurred during a time when the climate was different from that at present permitting surface runoff of fluids and standing bodies of water

convection in a catastrophic flood deposit as the mechanism for the giant polygons on mars a formational mechanism for the large scale polygons that are defined by intersecting fractures in the northern plains of mars is proposed in this work the presented model is based on rayleigh convection of interstitial water driven by an unstable density temperature gradient within a saturated porous medium catastrophic emplacement of water rich sediments into the martian northern plain basins could have provided a thick sedimentary layer in which rayleigh convection could have occurred convection within this active layer is proposed to have differentially thawed an underlying ice rich permafrost layer that had been at the planet s surface before being rapidly buried the resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid liquid interface morphology produced in terrestrial convective flow visualization studies the exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells which are estimated to have had width to depth ratios of between 3 4 and 4 5 subsequent stresses e g gravity and bending stresses would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by mcgill and hills 1992 additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large scale polygonal fractures visible in the viking orbiter and mars global surveyor images of the martian northern plains

latent outflow activity for western tharsis mars significant flood record exposed observations permitted by the newly acquired mars observer laser altimeter data have revealed a system of gigantic valleys northwest of the huge martian shield volcano arsia mons in the western hemisphere of mars northwestern slope valleys nsvs these features which generally correspond spatially to gravity lows are obscured by veneers of materials including volcanic lava flows air fall deposits and eolian materials geologic investigations of the tharsis region suggest that the system of gigantic valleys predates the construction of arsia mons and its extensive associated lava flows of mainly late hesperian and amazonian age and coincides stratigraphically with the early development of the outflow channels that debouch into chryse planitia similar to the previously identified outflow channels which issued tremendous volumes of water into topographic lows such as chryse planitia the nsvs potentially represent flooding of immense magnitude and as such a source of water for a northern plains ocean

differential subsidence and rebound in response to changes in water loading on mars possible effects on the geometry of ancient shorelines 1 if large liquid or solid water bodies existed in the past in martian basins such as argyre hellas and the northern lowland plains they would have represented massive surficial loads earth analogs suggest that the magnitudes of crustal displacements related to water loading and unloading would have varied spatially within and around affected basins it is likely that the effects of bathymetric irregularities on lithospheric flexure would have caused shoreline areas proximal to deep regions to be depressed and subsequently to rebound to a greater extent than shoreline areas located near shallow regions crustal and mantle inhomogeneities would have likely further contributed to spatial variation in water related subsidence and rebound simple two dimensional elastic flexure models suggest that martian shoreline features of common age and formed in association with a large ancient water body could vary in elevation today by hundreds of meters as a result of these differential effects examples of similar shoreline offsets on earth suggest that sets of martian strandline features will reflect the changing nature of loading through time

martian aeolian features and deposits comparisons with general circulation model results the development of a general circulation model gcm of mars atmosphere allows questions to be addressed concerning the relationships between near surface winds and the distribution of wind related features and deposits predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks yardangs and rock abundance on the surface the occurrence and orientation of bright streaks are well accounted for by the gcm results suggest that bright streaks form during southern hemisphere summer by hadley cell circulation in which dust is raised in the southern hemisphere carried northward at high altitudes then deposited in the wake of craters and other topographic obstacles by the descending hadley cell the reduction in the number of bright streaks southward from 30 n is interpreted to reflect the depletion of dust by near surface winds blowing to the south although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by gcm simulations a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season southern hemisphere summer yardang orientations do not match the gcm simulations for any season their orientation is attributed to either structural control in the rocks such as joint patterns or to a change in wind patterns from the time when the yardangs formed the global distribution of rocks on the surface is correlated well with predicted wind stress particularly during dust storm season the rocky areas are sites of strong winds suggesting that fine material is swept away by the wind leaving rocks and coarser material behind

origin of giant martian polygons extensive areas of the martian northern plains in utopia and acidalia planitiae are characterized by polygonal terrane polygonal terrane consists of material cut by complex troughs defining a pattern resembling mudcracks columnar joints or frost wedge polygons on earth however the martian polygons are orders of magnitude larger than these potential earth analogues leading to severe mechanical difficulties for genetic models based on simple analogy arguments plate bending and finite element models indicate that shrinkage of desiccating sediment or cooling volcanics accompanied by differential compaction over buried topography can account for the stresses responsible for polygon troughs as well as the large size of the polygons although trough widths and depths relate primarily to shrinkage the large scale of the polygonal pattern relates to the spacing between topographic elevations on the surface buried beneath polygonal terrane material geological relationships favor a sedimentary origin for polygonal terrane material but our model is not dependent on the specific genesis our analysis also suggests that the polygons must have formed at a geologically rapid rate

evidence for widespread aqueous sedimentation in the northern plains of mars high resolution imaging data sets were used to identify and investigate a discrete stratigraphic unit exposed in the walls of impact craters throughout chryse and acidalia planitiae mars the unique morphology and spectral signatures observed in this unit which include fine scale layering lensing pinching and elevated hydration signatures all indicate that this material was deposited in a suite of aqueous environments furthermore this unit s widespread distribution and relationship to regional topography suggests an origin from the circum chryse outflow channels while earlier studies have suggested that large quantities of outflow channel effluents are located throughout this region this analysis is the first to identify and characterize the outcrop scale morphology and spatial distribution of this extensive unit these observations imply that the northern plains of mars served as a global depocenter for immense volumes of water and sediment early in martian history

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

modeling tsunami propagation and the emplacement of thumbprint terrain in an early mars ocean the identification of lobate debris deposits in arabia terra along the proposed paleoshoreline of a former northern ocean has renewed questions about the existence and stability of ocean sized body of water in the early geologic history of mars the potential occurrence of impact generated tsunamis in a northern ocean was investigated by comparing the geomorphologic characteristics of the martian deposits with the predictions of well validated terrestrial models scaled to mars of tsunami wave height propagation direction runup elevation and distance for three potential sea levels our modeling suggests several potential impact craters 30 50 km in diameter as the source of the tsunami events within the complex topography of flat floored valleys and plateaus along the dichotomy boundary the interference of the multiple reflected and refracted waves that are observed in the simulation may explain the origin of the arcuate pattern that characterizes the thumbprint terrain

general geology and geomorphology of the mars pathfinder landing site the mars pathfinder mpf spacecraft landed on relatively young late hesperian early amazonian 3 1 0 7 ga plains in chryse planitia near the mouth of ares vallis images returned from the spacecraft reveal a complex landscape of ridges and troughs large hills and crater rims rocks and boulders of various sizes and shapes and surficial deposits indicating a complex multistage geologic history of the landing site after the deposition of one or more bedrock units depositional and erosional fluvial processes shaped much of the present landscape multiple erosional events are inferred on the basis of observations of numerous channels different orientations of many streamlined tails from their associated knobs and hills and superposition of lineations and streamlines medium and small scale features interpreted to be related to late stage drainage of floodwaters are recognized in several areas at the landing site streamlined knobs and hills seen in viking orbiter images support this inference as they seem to be complex forms partly erosional and partly depositional and may also indicate a series of scouring and depositional events that in some cases further eroded or partially buried these landforms although features such as these are cited as evidence for catastrophic flooding at ares vallis some of these features may also be ascribed to alternative primary or secondary depositional processes such as glacial or mass wasting processes close inspection of the landing site reveals rocks that are interpreted to be volcanic in origin and others that may be conglomeratic if such sedimentary rocks are confirmed fluvial processes have had a greater significance on mars than previously thought for the last several hundred million to few billion years eolian processes have been dominant dunes and dune like features ventifacts and deflation and exhumation features around several rocks probably are the most recent landforms the relatively pristine nature of the overall landscape at the mpf site suggests weathering and erosion processes on mars are exceptionally slow

possible ancient oceans on mars evidence from mars orbiter laser altimeter data high resolution altimetric data define the detailed topography of the northern lowlands of mars and a range of data is consistent with the hypothesis that a lowland encircling geologic contact represents the ancient shoreline of a large standing body of water present in middle mars history the contact altitude is close to an equipotential line the topography is smoother at all scales below the contact than above it the volume enclosed by this contact is within the range of estimates of available water on mars and a series of extensive terraces parallel the contact in many places

origin of the martian global dichotomy by crustal thinning in the late noachian or early hesperian the marked dichotomy in topography surface age and crustal thickness between the northern lowland and southern upland of mars has been explained as due to an initially inhomogeneous crust a single mega impact event several overlapping large basin impacts and first order convective overturn of the martian mantle all of the published hypotheses propose that the dichotomy was formed early in martian history before the end of the primordial heavy bombardment a primordial origin is inherent in the initial crustal inhomogeneity hypothesis and required for both impact hypotheses endogenic hypotheses are not so constrained geological data indicate episodes of fracturing and faulting in the late noachian and the early hesperian this fracturing and faulting occurred primarily within the northern lowland and along the boundary between lowland and highland igneous activity also peaked in the late noachian and early hesperian these data suggest a tectonic event near the noachian hesperian boundary characterized by enhanced heat loss and extensive fracturing including formation of the faults that define much of the highland lowland boundary we argue that the major result of this tectonic event was formation of the dichotomy by thinning of the crust above a large convection cell or plume

the circum chryse region as a possible example of a hydrologic cycle on mars geologic observations and theoretical evaluation the transection and superposition relationships among channels chaos surface materials units and other features in the circum chryse region of mars were used to evaluate relative age relationships and evolution of flood events channels and chaos in contact with one another were treated as single discrete flood carved systems some outflow channel systems form networks and are inferred to have been created by multiple flood events within some outflow channel networks several separate individual channel systems can be traced to a specific chaos which acted as flood source area to that specific flood channel individual flood carved systems were related to widespread materials units or other surface features that served as stratigraphic horizons chryse outflow channels are inferred to have formed over most of the perceivable history of mars outflow channels are inferred to become younger with increasing proximity to the chryse basin in addition outflow channels closer to the basin show a greater diversity in age the relationship of subsequent outflow channel sources to the sources of earlier floods is inferred to disfavor episodic flooding due to the progressive tapping of a juvenile near surface water supply instead we propose the circum chryse region as a candidate site of past hydrological recycling the discharge rates necessary to carve the circum chryse outflow channels would have inevitably formed temporary standing bodies of h2o on the martian surface where the flood waters stagnated and pooled the chryse basin is topographically enclosed these observations and inferences have led us to formulate and evaluate two hypotheses 1 large amounts of the sublimated h2o off the chryse basin flood lakes precipitated snowed onto the flood source highlands and this h2o was incorporated into the near surface recharging the h2o sources making possible subsequent deluges and 2 ponded flood water in chryse basin drained back down an anti basinward dipping subsurface layer accessed long the southern edge of the lake recharging the flood source aquifers h2o not redeposited in the flood source region was largely lost to the hydrologic cycle this loss progressively lowered the vitality of the cycle probably by now killing it our numerical evaluations indicate that of the two hypotheses we formulated the groundwater seep cycle seems by far the more viable optimally approximately 3 4 of the original mass of an ice covered cylindrical lake albedo 0 5 1 km deep 100 km radius draining along its rim for one quarter of its circumference into substrata with a permeability of 3000 darcies can be modeled to have moved underground on timescales of the order of 10 3 years before the competing mechanisms of sublimation and freeze down choked off further water removal once underground this water can travel distances equal to the separation between chryse basin and flood source sites in geologically short approximately 10 6 year scale times conversely we calculate that optimally only approximately 40 of the h2o carried from chryse can condense at the highlands and most of the precipitate would either collect at the base of the highlands lowlands scarp or sublimate at rates greater than it would accumulate over the flood source sites further observations from forthcoming missions may permit the determination of which mechanisms may have operated to recycle the chryse flood waters

characteristics and origin of polygonal terrain in southern utopia planitia mars results from mars orbiter laser altimeter and mars orbiter camera data giant polygons on mars with several kilometers in diameter were first observed in mariner 9 and viking orbiter images and their origin formation and evolution have remained enigmatic since that time new data obtained by the mars orbiter laser altimeter mola and the mars orbiter camera moc on board the mars global surveyor spacecraft now permit analysis of topography and morphology of the polygonal terrain in unprecedented detail mola data show that 1 giant polygonal terrain in utopia is located at the lower slopes of a basin structure that is the utopia basin 2 the onset of polygonal terrain in utopia is close to the same elevation in several profiles and lies at about the same elevation as a terrace which was interpreted as a shore line of an ancient body of standing water within the utopia basin proper 3 polygonal terrain occurs over a wide range of elevations on regional slopes of 0 1 4 the depths of the troughs range from 5 m to 115 m averaging about 30 m and tend to be greater toward the center of the utopia basin 5 the mean width of polygonal troughs is of the order of 2 km ranging from 0 5 to 7 5 km data from the mars orbiter camera moc indicate that 1 the troughs are generally broad graben like features with varying morphologies i e terraces and lobateness and dimensions widths and depths 2 trough morphology has been modified by aeolian processes 3 polygonal troughs are weakly interconnected at moc resolutions and there are no smaller polygons observed within the giant polygons 4 circular depressions which are probably related to subsurface collapse sometimes occur at the bottoms of polygonal troughs 5 small scale polygonal terrain on the ejecta blankets of young craters with fluidized ejecta in the investigated area exhibits different characteristics i e smaller size presence of rims greater degree of interconnections than giant polygons in the viking images we see that 1 old impact craters are increasingly buried with younger materials toward the basin center and that 2 a large number of superposed impact craters on polygonal terrain exhibit distinctive ejecta morphologies such as rampart ejecta blankets and single and double lobate ejecta blankets mola and moc observations are consistent with the formation of polygonal terrain in the area of a former standing body of water but polygon size seems too large to be readily accounted for by desiccation or freezing processes alone on the basis of the observed characteristics we propose that the giant polygons are primarily of tectonic origin being caused by uplift of the floor of the utopia basin there are several candidates for the cause of uplift 1 the removal of the load representing former standing bodies of water water thickness estimated for the utopia basin is about 1 km in this scenario removal of this load comparable to loads placed on terrestrial continental lithosphere by the laurentide and scandinavian ice sheets by loss of the water or ice could cause uplift of the floor and polygon formation 2 the freezing and expansion of residual water buried by sediments or in the near subsurface or 3 a combination of these from the discussion of alternative models in the light of the mola and moc data we conclude that formation of giant polygons by tectonic uplift of the basin floor is most likely and deserves further investigation

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

geochemical evolution of the northern plains of mars early hydrosphere carbonate development and present morphology it is likely that early in mars history abundant liquid water was available under a thick several bars carbon dioxide atmosphere this water could have formed an ocean located primarily in the lowlands of the northern hemisphere an equilibrium geochemical model of this ocean and its interactions with the atmosphere and regolith of mars was developed and the results of this model were used to discuss the evolution of the volatile budget of mars including the deposition of large carbonate beds on the northern plains differential solutional weathering of these carbonate beds may have caused the formation of some of the enigmatic features seen on the northern plains of mars such as the thumbprint terrain and enclosed depressions

valles marineris mars wet debris flows and ground ice abstract detailed study of the valles marineris equatorial troughs suggests that the landslides in that area contained water and probably were gigantic wet debris flows one landslide complex generated a channel that has several bends and extends for 250 km further support for water or ice in debris masses includes rounded flow lobes and transport of some slide masses in the direction of the local topographic slope differences in speed and emplacement efficiency between martian and terrestrial landslides can be attributed to the entrainment of volatiles on mars but they can also be explained by other mechanisms support that the wall rock contained water comes from the following observations 1 the water within the landslide debris must have been derived from wall rock 2 debris appears to have been transported through tributary canyons 3 locally channels emerged from the canyons 4 the wall rock apprarently disintegrated and flowed easily and 5 fault zones within the troughs are unusually resistant to erosion the study further suggests that in the equatorial region of mars material below depths of 400 800 m was not desiccated during the time of landslide activity within the last billion years of martian history therefore the martian ground water or groundice reservoir if not a relic from ancient times must have been replenished

combinations of processes responsible for martian impact crater layered ejecta structures emplacement 1 we utilized images and stereo derived topographic data acquired by the high resolution stereo camera hrsc and thermal emission imaging system themis images together with other data in order to study the geology of layered ejecta structures associated with relatively pristine martian impact craters the geomorphology and morphometric properties indicate their origin as complex combinations of a variety of impact processes the studied inner layered ejecta structures often exhibit ground hugging characteristics and many of them do not have topographic profiles expected from simple ballistic emplacement such profiles include ones that are plateau shaped or thickening outward we think that water rich fluidized flows driven by the momentum due to the impact and by gravity together with ballistic emplacement and vortex produced by the atmosphere ejecta curtain interaction were essential to the inner layered ejecta structure formation we hypothesize that the thinner outer layered ejecta structures were formed by various combinations of shockwave induced liquefaction of water rich near surface sediments ballistic emplacement of ejecta entraining water and strong winds expanding vapor vortex base surge related to the impact the contribution of each proposed layered ejecta structure formation mechanism should have been variable depending on the condition of the impact

formation of double ring circular grabens due to volumetric compaction over buried impact craters implications for thickness and nature of cover material in utopia planitia mars 1 throughout the polygonal terrain of utopia planitia are circular grabens inferred to overlie buried crater rims thirty four of the 37 circular grabens discovered in viking and thermal emission imaging system themis images southwest of the utopia basin 21 36 n 240 265 w have two nested rings while the remaining three have a single ring all 37 circular grabens bound topographic depressions whose surface relief scales directly with diameter suggesting differential compaction of cover material within the polygonal terrain the distance of doubled circular grabens from the center of the utopia basin scales directly with the spacing between the two rings implying a relation between ring spacing and cover thickness numerical models of horizontal shrinkage during volumetric compaction of material over crater rims show two maxima of horizontal normal tension on the surface these maxima where we would expect grabens to form move away from each other with increasing cover thickness the modeled spacings of stress maxima within 1 2 km thick cover are comparable to the graben spacing observed in southwest utopia planitia implying that cover thickness in this polygonal terrain may be 1 2 km thick where cover material is thin the proximity of the two normal stress maxima may only produce a single circular graben accounting for the observation that the three single ringed grabens are most distal to the center of the basin we contend that the correlation of shrinkage model results and observed ring spacing supports a wet sedimentary origin of polygonal terrain materials consistent with the past existence of standing water in the martian lowland

comparison of the north and south polar caps of mars new observations from mola data and discussion of some outstanding questions new high resolution data from the mars orbiter laser altimeter mola have provided detailed topographic maps for the north and south polar regions these new data allow one to compare the overall topography and geologic histories of the two polar regions and to highlight some specific outstanding questions in mars polar studies following earlier comparisons using viking and mars global surveyor data the new data show that the centers of symmetry of the polar cap deposits in map view which include both the layered terrain and residual ice are offset from the current rotational pole in antipodal directions offset in the north appears to be due to retreat of the polar materials from predominantly one direction 180 w lines of evidence for movement and melting in different forms e g lobes in young craters kettle like depressions candidate residual mantles overlying polar layered terrain and possible eskers have been seen at both poles the exact timing and causes of movement and melting is yet unknown differences in underlying topography large low flat depression in the north broad cratered high and edge of a large impact basin in the south may influence the accumulation flow and movement of polar material and the storage and movement of meltwater the small number of superposed craters has been interpreted to indicate a late amazonian age for both caps with the southern cap being somewhat older 7 15 106 years than the northern cap 100 103 years the late amazonian aged caps are surrounded and underlain by hesperian aged material indicating an apparent hiatus almost 3 byr in duration this apparent hiatus in the geologic record from the late hesperian to late amazonian at both poles may be accounted for in one of three ways 1 polar caps are recent events in the history of mars this scenario requires that conditions in the late amazonian changed to produce environments favorable for cap formation late in the history of mars or that polar wander brought the caps to their present position very recently 2 the polar caps are oscillating in this scenario caps are periodically deposited and then retreat and disappear possibly due to extremes in the obliquity cycle in this model the present caps are the latest example of cap deposition and represent the type of deposit that has come and gone numerous times in the amazonian 3 the present caps are old but have been renewed in this scenario the present caps have been in their current position for much of the amazonian but some process e g melting flow is periodically destroying preexisting craters to produce cap surfaces that appear very young in terms of crater retention ages documenting the nature of the emplacement history of the present polar deposits and distinguishing among these disparate scenarios for their history are among major challenges facing mars polar studies in the coming years

rift zone volcanism and associated cinder cone field in utopia planitia mars 1 we analyzed a small cone field in sw utopia planitia that shows striking similarities to volcanic rift zones on earth this is of particular interest as the study area lies off any of the volcanic centers of mars in the northern hemisphere lowlands and is surrounded by material of the amazonian aged vastitas borealis formation vbf we believe that the study area could be the first direct evidence for volcanic activity in utopia planitia prior to the resurfacing by vbf material the most striking characteristics that we observed are 1 a set of broad eruptive fissures showing signs of ongoing extension during cone formation 2 parallel dike swarms 3 magmatic intrusions and 4 a number of lava flows that have erupted from the fissures and pitted cones that surround a larger cone in the center of the study area and that are often associated with or aligned along the fissures and dikes cratering model ages indicate that the study area is of late noachian to early hesperian age and is thus distinctly older than the surrounding vbf falling into the time frame of the main phases of activity in the volcanic centers of syrtis major elysium planitia and the southern highlands

the utopia basin revisited regional slope and shorelines from mola profiles mola profiles indicate that utopia planitia including the utopia basin has been tilted northward by 0 025 since formation of the basin but no later than mid late hesperian this tilt could be a relic of the endogenic formation of the global dichotomy in late noachian to early hesperian by a process involving subcrustal erosion in the lowland the utopia basin survives as a deep circular depression within utopia planitia along its south flank are several horizontal or near horizontal terraces and benches that may be shorelines of an extensive northern lowland ocean and a more restricted lake within the utopia basin the large size up to 200 km wide of these putative shorelines represents a major geomorphic problem to be solved

mars chronology assessing techniques for quantifying surficial processes abstract currently the absolute chronology of martian rocks deposits and events is based mainly on crater counting and remains highly imprecise with epoch boundary uncertainties in excess of 2 billion years answers to key questions concerning the comparative origin and evolution of mars and earth will not be forthcoming without a rigid martian chronology enabling the construction of a time scale comparable to earth s priorities for exploration include calibration of the cratering rate dating major volcanic and fluvial events and establishing chronology of the polar layered deposits if extinct and or extant life is discovered the chronology of the biosphere will be of paramount importance many radiometric and cosmogenic techniques applicable on earth and the moon will apply to mars after certain baselines e g composition of the atmosphere trace species chemical and physical characteristics of martian dust are established the high radiation regime may pose a problem for dosimetry based techniques e g luminescence the unique isotopic composition of nitrogen in the martian atmosphere may permit a mars specific chronometer for tracing the time evolution of the atmosphere and of lithic phases with trapped atmospheric gases other mars specific chronometers include measurement of gas fluxes and accumulation of platinum group elements pge in the regolith putting collected samples into geologic context is deemed essential as is using multiple techniques on multiple samples if in situ measurements are restricted to a single technique it must be shown to give consistent results on multiple samples but in all cases using two or more techniques e g on the same lander will reduce error while there is no question that returned samples will yield the best ages in situ techniques have the potential to be flown on multiple missions providing a larger data set and broader context in which to place the more accurate dates

aeolian bedforms yardangs and indurated surfaces in the tharsis montes as seen by the hirise camera evidence for dust aggregates abstract hirise images of mars with ground sampling down to 25 cm pixel show that the dust rich mantle covering the surfaces of the tharsis montes is organized into ridges whose form and distribution are consistent with formation by aeolian saltation other dusty areas near the volcanoes and elsewhere on the planet exhibit a similar morphology the material composing these reticulate bedforms is constrained by their remote sensing properties and the threshold curve combined with the saltation suspension boundary both of which vary as a function of elevation atmospheric pressure particle size and particle composition considering all of these factors dust aggregates are the most likely material composing these bedforms we propose that airfall dust on and near the volcanoes aggregates in situ over time maybe due to electrostatic charging followed by cementation by salts the aggregates eventually reach a particle size at which saltation is possible aggregates on the flanks are transported downslope by katabatic winds and form linear and accordion morphologies materials within the calderas and other depressions remain trapped and are subjected to multidirectional winds forming an interlinked honeycomb texture in many places on and near the volcanoes light toned low thermal inertia yardangs and indurated surfaces are present these may represent duststone formed when aggregates reach a particle size below the threshold curve such that they become stabilized and subsequently undergo cementation

ancient oceans in the northern lowlands of mars evidence from impact crater depth diameter relationships 1 we present depth d and diameter d data for 2269 martian impact craters in the diameter range 6 216 km distributed over 11 52 106 km2 of terrain that samples several geologic settings and the full range of latitudes and elevations throughout the northern lowlands of mars our data indicate that there are three major crater types that fall into two major populations those craters that contain vastitis borealis formation vbf and those that do not the deepest type 1 craters comprise a late hesperian early amazonian age population that does not contain vbf type 2 type 3 and subdued type 1 craters comprise a population of hesperian age craters partially buried by the vbf the unique d d distribution of type 3 craters and photogeologic evidence suggest an erosional style for the vbf that requires sublimation processes indicating that the vbf contained a substantial amount of ice type 3 craters occur throughout the northern lowland plains at elevations below 2400 m if the vbf is a sedimentary deposit left by a large body of standing water in the northern lowlands of mars then the northern lowland plains contained a body of water with a volume of 6 107 km3 or the equivalent of a 430 m global ocean during the late hesperian early amazonian this also implies that the vbf contains 4 106 km3 of material in agreement with the estimated amount of material eroded from the outflow channels surrounding chryse basin and washed into the northern lowlands

episodic flood inundations of the northern plains of mars throughout the recorded history of mars liquid water has distinctly shaped its landscape including the prominent circum chryse and the northwestern slope valleys outflow channel systems and the extremely flat northern plains topography at the distal reaches of these outflow channel systems paleotopographic reconstructions of the tharsis magmatic complex reveal the existence of an europe sized noachian drainage basin and subsequent aquifer system in eastern tharsis this basin is proposed to have sourced outburst floodwaters that sculpted the outflow channels and ponded to form various hypothesized oceans seas and lakes episodically through time these floodwaters decreased in volume with time due to inadequate groundwater recharge of the tharsis aquifer system martian topography as observed from the mars orbiter laser altimeter corresponds well to these ancient flood inundations including the approximated shorelines that have been proposed for the northern plains stratigraphy geomorphology and topography record at least one great noachian early hesperian northern plains ocean a late hesperian sea inset within the margin of the high water marks of the previous ocean and a number of widely distributed minor lakes that may represent a reduced late hesperian sea or ponded waters in the deepest reaches of the northern plains related to minor tharsis and elysium induced amazonian flooding

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

sedimentary deposits in the northern lowland plains mars the lowland plains on mars have surfaces marked by large polygonal fracture patterns it was recently proposed that the fracture patterns were developed on sedimentary deposits from outflow channels we support this hypothesis because of the following observations 1 polygonal fracture patterns tend to occur in low areas on mars that apparently received influx of sediments the area of northern plains in which the fractures occur also forms a regional low 2 the fracture patterns are concentrated near reentrants of the plains projecting into the southern highlands not only are these reentrants associated with outflow channels but channels and polygonally fractured deposits have similar ages 3 sinuous ridges at the mouths of martian outflow channels resemble ridges in antarctic ice streams and ice shelves the similarity suggests that the martian material was transported from the southern highlands toward the northern plains as the antarctic material is transported from the continent toward the adjacent ocean overall it appears that a massive transfer of material took place midway in martian history either through the outflow channels or elsewhere along the northern highland scarp and that this material probably formed the deposits now characterized by polygonal fracture patterns

resurfacing of the martian highlands in the amenthes and tyrrhena region the southern cratered highlands of mars contain a large population of flat floored rimless craters which have previously been interpreted to have formed by aeolian mantling or flood volcanism neither of these geologic processes accurately explains the observed morphology or the crater statistics geologic mapping in the amenthes and tyrrhena region indicates that craters with this morphology occur on undulating intercrater materials near the dichotomy boundary and on more rugged materials farther into the highlands containing numerous ancient valley networks cumulative size frequency distribution curves indicate ages of n 5 790 early to middle noachian and n 5 540 middle noachian for the cratered plateau and cratered highland materials respectively opposite the observed stratigraphic relations for crater diameters 16 km the population of impact craters is consistent with stratigraphy but the population of smaller craters in the region indicates the importance of resultacing superposed fresh craters indicate a resultacing event that ceased at n 5 200 250 late noachian to early hesperian crater counts divided into 5 o latitudinal bins show an increase in the number of craters between the 8 and 50 km diameter range with increasing northerly latitudes suggesting that the resurfacing was not a single event statistical modelling of an erosive event capable of removing the continuous ejecta deposits from the craters eroding them to reduce the apparent diameter and simultaneously burying smaller eroded craters explains both the morphology of the flat floored rimless craters and their population distribution matching the slope of the modelled curves with that of the cratered highland materials suggests that up to 1400 m of erosion may have taken place in the highlands some of this eroded material probably remained locally burying the smaller craters later stripping of this material indicated by exposed layering and inverted topography has exhumed the smaller craters in the cratered plateau material resulting in the apparent age discrepancy determined from crater counts up to 1 0 km of material may have been removed by this later erosive event to explain the low density of ancient valley networks in the cratered plateau materials

mars formation and fate of a frozen hesperian ocean abstract late hesperian aged circum tharsis floods interpreted to have formed by catastrophic release of groundwater cut large channels and debouched significant quantities of water into the northern lowlands of mars the floods are thought by many to have formed an ocean of significant volume and depth encircled by contacts that have been interpreted as shorelines models of catastrophic groundwater release require a thick and continuous cryosphere with mean annual temperatures well below freezing much like those today in this environment the bodies of liquid formed by individual outflow events would have been very short lived undergoing rapid freezing we investigate the case where floods repeatedly flowed into the northern lowlands under climatic conditions that resemble those of the present day the water from each flood froze in a geologically short period of time to form an ice layer successive ice layers accumulated to form an ocean sized body of ice that filled the basin up to the 3650 contour thereby enclosing a 110 m global equivalent layer gel of water subsequent to the filling of the basin the ice slowly sublimated into the atmosphere to be lost to space or to accumulate in various surface and near surface cold traps such as the polar layered deposits where is this excess water today the presence of the thick global cryosphere meant that only minor amounts of water were lost from the surface back into the global groundwater system approximately 20 30 m gel of water is estimated to be at or near the surface today and exchanging with the atmosphere on geologic time scales this includes the polar layered deposits and deposits elsewhere at depths less than approximately 80 m below the exchangeable reservoir is a non exchangeable reservoir of unknown capacity present day loss rates to space fall far short of those needed to eliminate the mid hesperian ice ocean and those needed to cause the observed doubling of the d h of the exchangeable reservoir since the mid hesperian the discrepancy implies earlier loss rates must have been higher assuming a linear increase in loss rates because of the higher early euv output of the sun we estimate that for a present inventory of 30 m gel 42 m gel remains to be accounted for possibilities include greater dependence of losses of euv than assumed and enhanced losses during periods of high obliquity in addition large volumes of ice may be present near the surface at high latitudes outside the polar layered deposits as indicated by recent discoveries of ice layers in cliffs

utopia basin mars characterization of topography and morphology and assessment of the origin and evolution of basin internal structure recently obtained mars orbiter laser altimeter mola topography has permitted a new assessment of the morphology structure and history of utopia planitia the new topographic data convincingly demonstrate that the utopia region is an impact basin as originally proposed by mcgill 1989 whose major topographic expression is a circular 1 3 km deep depression 3200 km in diameter utopia basin is the largest easily recognizable impact structure in the northern hemisphere of mars and is the only portion of the northern lowlands that exhibits a distinct large scale impact signature its presence there and its ancient age verify that a significant part of the northern lowlands dates back to the noachian period using slope maps derived from gridded topography we have mapped a series of linear slope anomalies within the basin and have analyzed their origin these features can be classified into two groups one oriented dominantly radial to the basin and the other oriented dominantly circumferential the circumferential features are tens of kilometers wide and hundreds of kilometers long and appear to remain relatively constant with respect to elevation we explore end member hypotheses 1 that the features formed by the direct action of water ice or 2 that they are tectonic wrinkle ridges we interpret the majority of these features to be due to tectonic deformation primarily wrinkle ridge formation modified by later sedimentation associated with the emplacement of the outflow channels and the formation of the vastitas borealis formation on the basis of the characteristics of these features and their association with polygonal terrain thumbprint terrain smoothness of units and evidence of sedimentary deposits we find that our results support earlier hypotheses proposing that a significant volume of water occupied utopia basin during the late hesperian period of outflow channel formation utopia basin differs significantly in depth and degradation state from the deeper and fresher appearing hellas basin although the two are both noachian in age a significant part of this difference seems reasonably interpreted to be the result of the extensive sedimentary and volcanic infilling history of the northern lowlands

regional time predictable modeling in the hindukush pamir himalayas region abstract the seismic characteristic of hindukush pamir himalaya hph and its vicinity is very peculiar and has experienced many widely distributed large earthquakes recent work on the time dependent seismicity in the hindukush pamir himalayas is mainly based on the so called regional time predictable model which is expressed by the relation log t cm p a where t is the inter event time between two successive main shocks of a region and m p is the magnitude of the preceded main shock parameter a is a function of the magnitude of the minimum earthquake considered and of the tectonic loading and c is positive 0 3 constant in 90 of the cases with sufficient data parameter c was found to be positive which strongly supports the validity of the model in the present study a different approach which assumes no prior regionalization of the area is attempted to check the validity of the model nine seismic sources were defined within the considered region and the inter event time of strong shallow main shock were determined and used for each source in an attempt at long term prediction which show the clustering and occurrence of at least three earthquakes of magnitude 5 5 m s 7 5 giving two repeat times satisfying the necessary and sufficient conditions of time predictable model tp model further using the global applicability of the regional time and magnitude predictable model the following relations have been obtained log t t 0 19 m min 0 52 m p 0 29 log m 0 10 63 and m f 1 31 m min 0 60 m p 0 72 log m 0 21 01 where t t is the inter event time measured in years m min the surface wave magnitude of the smallest main shock considered m p the magnitude of preceding main shock m f the magnitude of the following main shock and m 0 the moment rate in each source per year these relations may be used for seismic hazard assessment in the region based on these relations and taking into account the time of occurrence and the magnitude of the last main shock in each seismogenic source time dependent conditional probabilities for the occurrence of the next large m s 5 5 shallow main shocks during the next 20 years as well as the magnitudes of the expected main shocks are determined

fluid expulsion in terrestrial sedimentary basins a process providing potential analogs for giant polygons and mounds in the martian lowlands abstract on earth burial of fine grained sediments in offshore passive margins e g underwater fans and deltas commonly results in fluid expulsion features including large scale polygonal fractures mud volcanoes and pockmarks comparison of resulting offshore polygons and mud volcanoes with giant polygons and high albedo mounds in the chryse acidalia region of mars shows the terrestrial and martian features to be similar in size morphology geologic context and general co occurrence within the same basin these similarities suggest that the process of terrestrial fluid expulsion may provide an analog that could link the giant polygons and mounds in chryse and acidalia to a single process moreover while the terrestrial offshore polygons and mud volcanoes commonly develop in the same basins these features do not necessarily occur in exactly the same locations within those basins as they are independent responses to compaction and dewatering thus the fluid expulsion analog does not require that the martian giant polygons and mounds have identical distributions this is the situation in chryse and acidalia where the giant polygons and mounds are extensively developed and generally have overlapping distributions but where each set of features may occur in places without the other this fluid expulsion analog is enhanced by the fact that giant polygons and mounds in chryse and acidalia co occur in a regional sense and in a geologic setting that is consistent with a fluid expulsion model of formation implications of this analog may impact our view of the role of water in the depositional history of the martian lowlands

the evolution of lacustrine environments on mars is mars only hydrologically dormant abstract this study surveys the evolution of martian impact crater paleolakes through time by establishing their age comparing their locations and describing the formation of lacustrine sedimentary structures and features over time we explore their meaning in terms of global climate changes but also on local and regional scales we observe a co location between recent impact crater paleolakes and regions where gcm modeling shows that mars is currently experiencing days above triple point and below boiling point of water some source areas show morphologies that could be consistent with ancient glacier features in the argyre basin darwin crater region in locations that are also consistent with gcm models of past snow precipitation on mars we propose that at least for some paleolakes our results are best explained by recent and abundant aqueous activity on mars with some meteorological contribution these results are supported by other recent findings on martian meteorite ages by the analysis of new mgs data showing recent volcanic and fluvial activity and by climate modeling they point toward the possibility that mars currently is only hydrologically dormant and that there is a potential for hydrological activity to be generated again in the future following changes in the planet s orbital parameters

spatial distribution of putative water related features in southern acidalia cydonia mensae mars abstract many putative water related features exist in the northern lowlands of mars these features may provide clues to the abundance and timing of water or ice that existed there in the past the cydonia mensae and southern acidalia area was chosen as the study area owing to the abundance of two of these features giant polygons and pitted cones in addition a section of the deuteronilus shoreline is located there the abundance and close proximity of the features makes this area an excellent place to study the spatial relationships between these landforms as well as the morphological characteristics of pitted cones the features were mapped into a gis for spatial analyses the highest densities of pitted cones and giant polygons are adjacent but distinctly separated by a knobby ridge that is surrounded by the deuteronilus putative shoreline pitted cones were measured and examined to determine if a classification by morphology is possible but the results were inconclusive statistical tests on pit to cone diameter ratios and tests of surface temperatures of cone material suggest but do not verify a single cone origin the various shapes sizes and putative ages of pitted cones may be attributed to temporal variation in emplacement and spatial variation in material properties among the possible scenarios put forth for pitted cone genesis on mars two are likely candidates in cydonia mensae 1 the sublimation of a cold based glacier and 2 a buried lens of methane and or co2 clathrates

evidence of volcanic and glacial activity in chryse and acidalia planitiae mars abstract chryse and acidalia planitiae show numerous examples of enigmatic landforms previously interpreted to have been influenced by a water ice rich geologic history these landforms include giant polygons bounded by kilometer scale arcuate troughs bright pitted mounds and mesa like features to investigate the significance of the last we have analyzed in detail the region between 60 n 290 e and 10 n 360 e utilizing hirise high resolution imaging science experiment images as well as regional scale data for context the mesas may be analogous to terrestrial tuyas emergent sub ice volcanoes although definitive proof has not been identified we also report on a blocky unit and associated landforms drumlins eskers inverted valleys kettle holes consistent with ice emplaced volcanic or volcano sedimentary flows the spatial association between tuya like mesas ice emplaced flows and further possible evidence of volcanism deflated flow fronts volcanic vents columnar jointing rootless cones and an extensive fluid rich substratum giant polygons bright mounds rampart craters allows for the possibility of glaciovolcanic activity in the region landforms indicative of glacial activity on chryse acidalia suggest a paleoclimatic environment remarkably different from today s climate changes on mars driven by orbital obliquity changes or giant outflow channel activity could have resulted in ice sheet related landforms far from the current polar caps

late hesperian plains formation and degradation in a low sedimentation zone of the northern lowlands of mars abstract the plains materials that form the martian northern lowlands suggest large scale sedimentation in this part of the planet the general view is that these sedimentary materials were transported from zones of highland erosion via outflow channels and other fluvial systems the study region the northern circum polar plains south of gemini scopuli on planum boreum comprises the only extensive zone in the martian northern lowlands that does not include sub basin floors nor is downstream from outflow channel systems therefore within this zone the ponding of fluids and fluidized sediments associated with outflow channel discharges is less likely to have taken place relative to sub basin areas that form the other northern circum polar plains surrounding planum boreum our findings indicate that during the late hesperian sedimentary deposits produced by the erosion of an ancient cratered landscape as well as via sedimentary volcanism were regionally emplaced to form extensive plains materials within the study region the distribution and magnitude of surface degradation suggest that groundwater emergence from an aquifer that extended from the arabia terra cratered highlands to the northern lowlands took place non catastrophically and regionally within the study region through faulted upper crustal materials in our model the margin of the utopia basin adjacent to the study region may have acted as a boundary to this aquifer partial destruction and dehydration of these late hesperian plains perhaps induced by high thermal anomalies resulting from the low thermal conductivity of these materials led to the formation of extensive knobby fields and pedestal craters during the early amazonian the rates of regional resurfacing within the study region decreased significantly perhaps because the knobby ridges forming the eroded impact crater rims and contractional ridges consisted of thermally conductive indurated materials thereby inducing freezing of the tectonically controlled waterways associated with these features this hypothesis would explain why these features were not completely destroyed during the late amazonian high obliquity conditions may have led to the removal of large volumes of volatiles and sediments being eroded from planum boreum which then may have been re deposited as thick circum polar plains transition into low obliquity 5 myr ago may have led to progressive destabilization of these materials leading to collapse and pedestal crater formation our model does not contraindicate possible large scale ponding of fluids in the northern lowlands such as for example the formation of water and or mud oceans in fact it provides a complementary mechanism involving large scale groundwater discharges within the northern lowlands for the emplacement of fluids and sediments which could have potentially contributed to the formation of these bodies nevertheless our model would spatially restrict to surrounding parts of the northern plain either the distribution of the oceans or the zones within these where significant sedimentary accumulation would have taken place

chasma boreale mars topographic characterization from mars orbiter laser altimeter data and implications for mechanisms of formation 1 chasma boreale a large reentrant in the north polar cap of mars is distinct in scale detailed topography and orientation from the spiraling troughs that characterize the majority of the polar cap we use new high resolution mars orbiter laser altimeter mola data and mars orbiter camera moc and viking images of the chasma region to assess hypotheses of origin of chasma boreale these hypotheses include formation by glacial flow and ablation by eolian processes such as katabatic winds and sublimation by outflow of meltwater or by a combination of two or more of these processes we find that these new data support initial formation by outflow of meltwater with later modification by katabatic winds and sublimation on the basis of our analysis we suggest a possible scenario in which outflow has occurred in several stages the outflow appears to have begun near an enclosed depression at the head of the chasma meltwater migrated within and below the ice down the regional slope and eventually broke out to the surface removal of material by melting caused subsidence and erosion of the polar deposits forming the chasma which has subsequently undergone modification by eolian and sublimation processes the outflow deposited most of its sediment in the form of a lobe that stratigraphically overlies the polygonal plains mapped at the mouth of the chasma and scoured some of the circumpolar sediment mantle in the surrounding region the lowest portions of the north polar basin received the rest of the sediment as a deposit a few meters thick mola data also reveal evidence for similar events of smaller magnitude elsewhere on the margins of the polar cap

martian impact craters correlations of ejecta and interior morphologies with diameter latitude and terrain abstract the premise of this study is that global analysis of crater morphologies can discriminate between the effects of impact energy atmosphere and subsurface volatiles based on the correlation between morphology and latitude diameter and terrain this study focuses on seven ejecta and nine interior morphologies associated with 3819 craters 8 km in diameter distributed across the entire martian surface this data set is sufficiently large to provide statistically viable results on a global scale the results of the analyses indicate that changes in ejecta and interior morphology correlate with increases in crater diameter excavation depths corresponding to these diameters are calculated from depth diameter relationships and are compared to the theoretical distribution of subsurface volatiles the different ejecta morphologies can be described by impact into material with varying proportions of volatiles and the latidudinal variations seen for rampart crater morphologies correlate well with the proposed latitude depth relationship for ice and brines across the planet many of the interior structres show distributions indicative of terrain dependent influences for example the concentrations of central pit craters around ancient impact basins and on alba patera suggest that volatiles preferentially collect in these areas however central peak and peak ring interior morphologies show little relationship to planetary properties and probably result from changes in impact energy thus many of the unique morphologies associated with martian impact craters result from the presence of subsurface volatiles

clues to the lithospheric structure of mars from wrinkle ridge sets and localization instability 1 wrinkle ridges are a manifestation of horizontal shortening in planetary lithospheres for which deformation is localized on faults that underlie individual ridges in ridged plains of mars such as solis planum or lunae planum wrinkle ridges are spaced 40 km apart whereas in the martian northern lowlands where ridges are identified only in mars observed laser altimeter mola altimetric data the ridge spacing is at least 80 km we attribute ridge spacing to an instability of the lithosphere under horizontal compression the localization instability which results in periodically spaced faults montesi and zuber 2003a links the difference of ridge spacing in the northern lowlands and in the highland ridged plains to the difference of crustal thickness via the depth of the brittle ductile transition bdt in solis and lunae plana where the crust is 50 to 60 km thick the crust may be ductile at depth limiting faulting to the bdt of crustal rocks in the lowlands the crust is only about 30 km thick and may be brittle throughout thus the depth of faulting may be controlled by the bdt of mantle rocks which is roughly a factor of two deeper than that of crustal rocks the geotherm can be identical in both regions at 12 3 k km 1 although differences of a few k km 1 can be accommodated within this model the heat flux implied by this geotherm is similar to the heat produced by radiogenic decay 3 gyr ago our analysis provides a rheological explanation for the difference in spacing between ridges in the highlands and the lowlands in contrast to the suggestion of head et al 2002 who proposed that alternating lowlands ridges are buried by sediments in addition finite element models that use the lithospheric structure deduced from ridge spacing show that modest gradients of crustal thickness or heat flux across a ridged plains favor the formation of faults dipping toward high elevation areas as may be the case in solis planum golombek et al 2001

putative shorelines in northern arabia terra mars 1 three putative shorelines first proposed by parker et al 1989 are topographically and morphologically evaluated within a 700 000 km2 study area in northern arabia terra mars results are consistent with a shoreline interpretation for the arabia and deuteronilus contacts but do not support the proposed acidalia shoreline the arabia contact follows an equipotential surface with a mean elevation of 3707 m and a mean deviation of 13 m for deuteronilus results suggest that the originally proposed shoreline represents two distinct regional shorelines because two separate portions of the original deuteronilus contact approximate equipotential surfaces of 4200 m 5 m and 4000 m 6 m for both the deuteronilus and arabia contacts there is geomorphic evidence for erosion and some landforms are similar to analogous terrestrial coastal landforms these results permit but do not prove the past existence of an ocean ponded within the northern lowlands possibly as recently as the amazonian

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

resurfacing history of the northern plains of mars based on geologic mapping of mars global surveyor data 1 geologic mapping of the northern plains of mars based on mars orbiter laser altimeter topography and viking and mars orbiter camera images reveals new insights into geologic processes and events in this region during the hesperian and amazonian periods we propose four successive stages of lowland resurfacing likely related to the activity of near surface volatiles commencing at the highland lowland boundary hlb and progressing to lower topographic levels as follows highest elevations indicated stage 1 upper boundary plains early hesperian 2 0 to 2 9 km stage 2 lower boundary plains and outflow channel dissection late hesperian 2 7 to 4 0 km stage 3 vastitas borealis formation vbf surface late hesperian to early amazonian 3 1 to 4 1 km and stage 4 local chaos zones early amazonian 3 8 to 5 0 km at acidalia mensa stage 2 and 3 levels may be lower 4 4 and 4 8 km respectively contractional ridges form the dominant structure in the plains and developed from near the end of the early hesperian to the early amazonian geomorphic evidence for a northern plains filling ocean during stage 2 is absent because one did not form or its evidence was destroyed by stage 3 resurfacing remnants of possible amazonian dust mantles occur on top of the vbf the north polar layered deposits appear to be made up of an up to kilometer thick lower sequence of sandy layers early to middle amazonian in age overlain by late amazonian ice rich dust layers both units appear to have outliers suggesting that they once were more extensive

the stratigraphy and history of mars northern lowlands through mineralogy of impact craters a comprehensive survey the basin filling materials of the northern lowlands which cover approximately one third of mars surface record the long term evolution of mars geology and climate the buried stratigraphy was inferred through analyses of impact crater mineralogy detected using data acquired by the compact reconnaissance imaging spectrometer for mars examining 1045 impact craters across the northern lowlands we find widespread olivine and pyroxene and diverse hydrated hydroxylated minerals including fe mg smectite chlorite prehnite and hydrated silica the distribution of mafic minerals is consistent with infilling volcanic materials across the entire lowlands 1 4 10 7 km 3 indicating a significant volume of volatile release by volcanic outgassing hydrated hydroxylated minerals are detected more frequently in large craters consistent with the scenario that the hydrated minerals are being excavated from deep basement rocks beneath 1 2 km thick mafic lava flows or volcaniclastic materials the prevalences of different types of hydrated minerals are similar to statistics from the southern highlands no evidence of concentrated salt deposits has been found which would indicate a long lived global ocean we also find significant geographical variations of local mineralogy and stratigraphy in different basins geological provinces independent of dust cover for example many hydrated and mafic minerals are newly discovered within the polar scandia region 60 n and chryse planitia has more mafic mineral detections than other basins possibly due to a previously unrecognized volcanic source

chryse planitia mars topographic configuration outflow channel continuity and sequence and tests for hypothesized ancient bodies of water using mars orbiter laser altimeter mola data many of the largest and most prominent outflow channels on mars debouch into chryse planitia pre mars global surveyor topographic data show chryse to be a closed depression almost 2000 km in diameter new mars orbiter laser altimeter mola data reveal the following 1 chryse is not a locally closed basin but instead opens into the north polar basin 2 the highly distinctive morphology of the six largest predominantly hesperian aged channels kasei maja simud tiu ares and mawrth disappears into the northern lowlands at average elevations that all occur within less than 170 m of a mean elevation of 3742 sd 153 m over a lateral distance in excess of 2500 km 3 the elevations where the distinctive morphology of each channel disappears all fall within 190 m of contact 2 a boundary mapped by parker et al 1993 and interpreted to represent an ancient shoreline and the mean elevation values of contact 2 and circum chryse channel termini fall within 18 m of each other in contrast the termini of seven later amazonian aged channels emerging from elysium into utopia planitia are spread over a vertical range of 1500 m 4 topographic evidence of the continuation of some of the outflow channels can be observed for distances of 250 450 km into the north polar basin but the morphology is subdued and distinctly different 5 the nature of this less distinctive topography and its crosscutting relationships show that simud and tiu are likely to represent the youngest activity specifically crosscutting ares valles 6 the distinctive change in channel morphology is consistent with rapid loss of energy encountered at base level subaerial submarine boundary and emplacement into a shallow submarine environment channel characteristics lack of distinctive deltas or lobes and continuation of subdued channel morphology suggest hyperpychnal flow and the possibility of density turbidity currents estimates of the volumes of individual channel events are wide ranging the minimum volume estimates of carr 1996 suggest that 46 such events would be required to fill the basin to the level of contact 2 and thus that the channels may have emptied into an existing standing body of water volume estimates of baker et al 1991 assume that single individual events may have filled the basin to the level of contact 2 thus requiring significant water loss between events and refilling during subsequent events to essentially the same level in both end member cases these observations are consistent with the presence of large standing bodies of water in the northern lowlands in hesperian early amazonian times

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick