ice lubricated gravity spreading of the olympus mons aureole deposits abstract gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of olympus mons detachment sliding could have occurred around the volcano if either pore fluid pressures were exceptionally high greater than 90 or the rocks had very low resistance to shear about 1 105 pa or 1 bar because of the vast areal extent and probable shallow depth of the detachment zone development of ubiquitous high pore fluid pressures beneath aureole forming material was unlikely however a zone of sufficiently weak material consisting of about 10 interstitial or interbedded ice could have been present if so a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer according to this model extensional deformation would have occurred near the shield and compressional deformation in its distal parts proximal grabens and distal corrugations on aureole surfaces support this model a submarine slide at kitimat arm british columbia is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits ground ice processes have been considered the cause of many geologic features on mars a 3 average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere ice may have been deposited in higher concentrations below the aureole forming material the source of the ice could have been juvenile water circulated hydrothermally by olympus mons volcanism the basal scarp of olympus mons apparently demarcates the transition between the upper stable part of the shield and its lower part that decoupled and formed the aureole deposits this transition may reflect a change in the bulk shear strength of the shield caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano other martian volcanoes exhibit virtually no evidence of similar large scale gravity spreading and basal scarps perhaps such evidence if it existed has been buried by lava flows or perhaps the smaller size of other volcanoes did not permit the development of these features

eruption history of the elysium volcanic province mars abstract volcanism has played a significant role in shaping the surface of mars volatiles released during eruptions profoundly altered the composition and density of the martian atmosphere in the past quantifying the amounts of volcanic outgassing has been attempted regionally and globally however volume estimates of erupted volcanic material in time are still poorly constrained here we show the first eruption frequency record of a volcanic region the elysium volcanic province which is the second largest volcanic province on mars studied lava flows show model ages ranging from 3 4 ga to 60 ma together with observed resurfacing ages the visible record of volcanic activity extends back to 3 9 ga based on our 190 model ages continuous volcanic activity is apparent with a major peak at 2 2 ga in the last 1 gyr the activity rapidly waned although the majority of volcanic material including volatiles released to the atmosphere erupted within a short time span of less than 200 ma activity continued until the very recent past extrapolating the eruption record it appears likely that this region of mars is still volcanically active today our derivation of the eruption record has profound implications for global thermal and atmospheric modeling indicating sustained heat production melt generation and magma ascent at a single location over most of the planet s geological history

a global view of martian surface compositions from mgs tes thermal emission spectrometer tes data from the mars global surveyor mgs are used to determine compositions and distributions of martian low albedo regions two surface spectral signatures are identified from low albedo regions comparisons with spectra of terrestrial rock samples and deconvolution results indicate that the two compositions are a basaltic composition dominated by plagioclase feldspar and clinopyroxene and an andesitic composition dominated by plagioclase feldspar and volcanic glass the distribution of the two compositions is split roughly along the planetary dichotomy the basaltic composition is confined to older surfaces and the more silicic composition is concentrated in the younger northern plains

results from the mars global surveyor thermal emission spectrometer the thermal emission spectrometer spectra of low albedo surface materials suggests that a four to one mixture of pyroxene to plagioclase together with about a 35 percent dust component provides the best fit to the spectrum qualitative upper limits can be placed on the concentration of carbonates 10 percent olivine 10 percent clay minerals 20 percent and quartz 5 percent in the limited regions observed limb observations in the northern hemisphere reveal low lying dust hazes and detached water ice clouds at altitudes up to 55 kilometers at an aerocentric longitude of 224 degrees a major dust storm developed in the noachis terra region the south polar cap retreat was similar to that observed by viking

early views of the martian surface from the mars orbiter camera of mars global surveyor high resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms dunes sandsheets and drifts are prevalent and exhibit a range of morphology composition inferred from albedo and age as seen in occurrences of different dune orientations at the same location steep walls of topographic depressions such as canyons valleys and impact craters show the martian crust to be stratified at scales of a few tens of meters the south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non volatile components low resolution regional views of the planet provide synoptic observations of polar cap retreat condensate clouds and the lifecycle of local and regional dust storms

fate of outflow channel effluents in the northern lowlands of mars the vastitas borealis formation as a sublimation residue from frozen ponded bodies of water 1 we analyze the fate of the hesperian aged outflow channel effluents emplaced into the northern lowlands of mars we have modeled the evolution of these effluents under the assumption that they were emplaced under a range of atmospheric conditions comparable to those of today and thought to have prevailed in the hesperian under these conditions we find that the evolution of the sediment loaded water after it left the channels includes three phases phase 1 emplacement and intensive cooling violent emplacement of water followed by a short period of intensive evaporation from the surface and near surface layer and intensive convection during this phase the water maintained and redistributed its large suspended sediment load water vapor strongly influenced the climate at least for a geologically short time when the temperature of the water reached the temperature of the maximum density or the freezing point boiling and intensive convection ceased and the water deposited the sediments phase 2 freezing solid geologically rapid freezing of the water body accompanied by weak convective water movement occurred over a period of the order of 104 years phase 3 sublimation and loss this period involved sublimation of the ice and lasted longer than the freezing phase the rate and latitudinal dependence of the sublimation as well as the location of water vapor condensation crucially depend on the planetary obliquity climate and sedimentary veneering of the ice phase 3 would have been very short geologically 105 106 years if an insulating sedimentary layer did not build up rapidly if such an insulating layer did form rapidly sublimation could cease and residual ice hundreds of meters thick could remain below the surface today the northern lowlands of mars are largely covered by the late hesperian aged vastitas borealis formation vbf which has sharp boundaries clearly seen in the map of kilometer scale roughness and a distinctive kilometer scale roughness signature we examine detrended topography data and find evidence that the vbf is underlain at very shallow depths by an early hesperian ridged volcanic plains substrate rather than frozen water deposits remaining from the outflow channel events analysis of the vbf roughness characteristics suggests at least 100 m thickness of sediments on top of the underlying volcanic ridged plains the total inferred volume of the vbf material approximately corresponds to the volume of material removed from the outflow channels these results support a model in which the vastitas borealis formation predominantly represents the sedimentary residue remaining after the sediment laden water effluents of the outflow channels ponded in the northern lowlands and rapidly froze solid and sublimed the distinctive facies of the vbf are interpreted to be related to the freezing sublimation and residue of the outflow channel effluents ridged facies are dominantly marginal and are interpreted to be related to ice sheet lateral retreat knobby facies occur throughout and are interpreted to be due to a variety of causes including dewatering de icing and brine related processes and kame like ice residues grooved facies are interpreted to represent postsublimation uplift and fracturing due to load removal the mottled facies may represent bright ejecta whose albedo is related to buried sedimentary or evaporitic residues presently the most likely sites to find frozen remnants of the hesperian ocean are below the floors of stealth craters underlying the vbf on the basis of these findings and interpretations we make predictions for the fate of the outflow channel water vapor and the nature of the martian hydrologic cycle during the hesperian if noachian aged oceans existed conditions at that time would be similar to those described for a hesperian ocean as soon as a global cryosphere was formed if any residual deposits remain in the northern lowlands from a proposed noachian ocean they would lie below both the vbf and the underlying sequence of hesperian ridged plains

the morphologies of volcanic landforms at central elysium planitia evidence for recent and fluid lavas on mars abstract this paper focuses on physical parameters flow rates and rheological properties of lava flows observed in the central elysium planitia cep region of mars the flows are modeled as newtonian fluids using the jeffrey s equation and the concept of graetz number or alternatively as bingham fluids in addition to these approaches a theoretical model of the shape of shield volcanoes based on the solution for the porous flow of an unconfined aquifer is applied to 5 shields providing independent quantifications of rheological variations between the shields this analysis indicates that of the five volcanoes studied two are partially buried by lava postdating their formation a result which has been confirmed independently in one case by high resolution images our observations reveal that two types of lava flows may be found in the cep region the first group is composed of large lava flows with viscosities around 2 5 10 5 pa s or yield strengths ranging from 100 to 500 pa the second group includes small lava flows of the shield volcanoes and large leveed lava channels on the plains with viscosities below 103 pa s or yield strengths less than 200 pa when compared with other volcanic regions on mars investigated with similar approaches these latter values are at present the lowest inferred for martian lava flows several hypotheses for the formation of these lavas are discussed in the context of cep given that low viscosity can be the result of 1 high temperature 2 low crystal content 3 low si abundance of the liquid phase and or 4 the presence of dissolved volatiles two scenarios are considered in the first one it is demonstrated that low viscosity lavas of low silica content can be produced in the context proposed by schumacher and breuer schumacher s breuer d 2007 geophys res lett 34 l12202 for recent volcanism however geochemical maps derived from grs measurements do not provide support for anomalously low silica concentrations in this region in the second scenario a water rich magma is proposed although arguments in favor of a water rich mantle source below the cep are not available at the present time

medusae fossae formation new perspectives from mars global surveyor 1 the nature and origin of the medusae fossae formation mff on mars has been debated since the return of the first viking images the mff s young age distinctive surface texture and lack of obvious source have prompted multiple hypotheses for its origin this study uses data from the mars global surveyor mgs mission to examine the mff at all available scales we discuss and quantify observations from mars orbiter laser altimeter mola topography and mars orbiter camera moc images to better constrain the origin of the mff topographic grid estimates yield a present extent of 2 1 106 km2 and a volume of 1 4 106 km3 however remnant yardang deposits observed far from the thicker lobes of mff material suggest that it may have once covered up to 5 106 km2 we do not find compelling evidence for extensive fluvial reworking of the mff however in several regions buried channels are apparent in the mff because the formation is draped over underlying topography layering is apparent at all scales from submeter to hundreds of meters with variable resistance to weathering continuity of layers appears to be local to regional but not likely formation wide yardangs form both parallel and bidirectional patterns with resistant layers and jointing probably influencing their orientations a comparative study of mff regional topography and surface expression indicates that the mff is quantitatively dissimilar to martian polar layered deposits the material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin

the evolution of impact basins cooling subsidence and thermal stress potentially important contributors to the topography and tectonics of multi ring impact basins are the thermal contraction and thermal stress that accompany the loss of heat emplaced during basin formation heat converted from impact kinetic energy and contributed from the uplift of isotherms during cavity collapse are important components in the energy budget of a newly formed basin that the subsequent cooling may have been an important factor in the tectonic evolution of the orientale basin is suggested by the deep central depression and by a surrounding region of extensive fissuring to test these concepts we develop models for the anomalous temperature distribution immediately following basin formation and we calculate the resulting elastic displacement and stress fields that then would accompany cooling of the basin region all models predict subsidence of the basin floor and a near surface stress field consistent with fissuring in addition the rates of cooling and of accumulation of thermal stress are in agreement with the inferred timing of fissure formation in orientale the sensitivity of the predicted displacements and stresses to the initial temperature field allows us to place bounds on the quantity and distribution of impact heat emplaced during basin formation in order to be consistent with the observed topography and the distribution of fissures in the orientale basin the buried heat deposited during the basin forming event was between 1032 and 1033 erg it is likely that most of this heat was concentrated within a distance of 100 200 km from the point of impact

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

mars radar mapping strong backscatter from the elysium basin and outflow channel abstract radar reflectivity maps of mars obtained at arecibo in 1990 using a modified delay doppler technique have revealed strong depolarized echoes coming from the elysium flood basin and outflow channel as well as from elysium mons this result is consistent with recent studies which show that much of the basin channel floor is covered with lava flows

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

wrinkle ridges of arcadia planitia mars wrinkle ridges of arcadia planitia were examined to determine their morphology spatial distribution and the amount of crustal shortening and strain they accommodate ridges trend generally northward but their orientation and distribution are strongly controlled by the relief of the underlying knobby material ridges begin or end at inselbergs of older terrain and are associated with buried craters arcadia planitia ridges have an average width of 3425 m and accommodate an average folding shortening of 3 m and a faulting shortening of 55 m mean total shortening is 57 m three east west transects were constructed at 20 25 and 28 n to estimate regional shortening and strain average total shortening across the transects is about 900 m corresponding to a regional compressive strain of 0 06 the total shortening and compression across arcadia planitia are less than in lunae planum faults associated with the arcadia ridges are inferred to have a westward dip compared with an eastward dip for lunae planum ridges the generally levels of compression and symmetric orientation of the ridges suggest a regionally organized stress system differences in the shortening and strain between lunae planum and arcadia planitia may reflect the effects of local lithology or azimuthal variations in the stress field

the relation of catastrophic flooding of mangala valles mars to faulting of memnonia fossae and tharsis volcanism detailed stratigraphic relations indicate two coeval periods of catastrophic flooding and tharsis centered faulting producing memnonia fossae in the mangala valles region of mars major sequences of lava flows of the tharsis montes formation and local lobate plains flows were erupted during and between these channeling and faulting episodes first late hesperian channel development overlapped in time the tharsis centered faulting that trends north 75 to 90 e next late hesperian early amazonian flooding was coeval with faulting that trends north 55 to 70 e in some reaches resistant lava flows filled the early channels resulting in inverted channel topography after the later flooding swept through both floods likely originated from the same graben which probably was activated during each episode of faulting faulting broke through groundwater barriers and tapped confined aquifers in higher regions west and east of the point of discharge the minimum volume of water required to erode mangala valles about 5 1012 m3 may have been released through two floods that drained a few percent pore volume from a relatively permeable aquifer the peak discharges of the floods may have lasted from days to weeks the perched water discharged from the aquifer may have been produced by hydrothermal groundwater circulation induced by tharsis magmatism tectonic uplift centered at tharsis montes and compaction of saturated crater ejecta due to loading by lava flows

internal structure and early thermal evolution of mars from mars global surveyor topography and gravity topography and gravity measured by the mars global surveyor have enabled determination of the global crust and upper mantle structure of mars the planet displays two distinct crustal zones that do not correlate globally with the geologic dichotomy a region of crust that thins progressively from south to north and encompasses much of the southern highlands and tharsis province and a region of approximately uniform crustal thickness that includes the northern lowlands and arabia terra the strength of the lithosphere beneath the ancient southern highlands suggests that the northern hemisphere was a locus of high heat flow early in martian history the thickness of the elastic lithosphere increases with time of loading in the northern plains and tharsis the northern lowlands contain structures interpreted as large buried channels that are consistent with northward transport of water and sediment to the lowlands before the end of northern hemisphere resurfacing

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

elysium planitia lava flows crater count chronology and geological implications mars global surveyor mgs and viking images allow analysis of chronological and geological relations among lava flows in southern elysium planitia based on crater populations mgs and viking images clearly show morphological features of lava flows with some extremely sparsely cratered young flow units atop somewhat older surfaces there is no evidence of substantial dust mantling on the young flows and hence we infer that the crater populations date not sediment accumulation but the lava flows themselves the youngest flows have some of the lowest crater densities that we have seen on mars some 1 of lunar mare values at crater diameters below about 180 to 500 m we infer that thin scattered volcanic flows some tens of meters thick have been emplaced atop stratigraphic units within the last 100 myr and possibly within the last 10 myr volcanism is thus a continuing process in the recent geologic history of mars and this must constrain geophysical models of the planet

recent flood lavas in the elysium region of mars abstract a vast area of smooth plains in southeastern elysium here referred to as the cerberus formation is interpreted to be of volcanic origin surface morphology lobate edges of the unit the identification of vents low shields and the embayment relation of the unit with adjacent older units all suggest a volcanic origin the plains were formed by the eruption of low viscosity lavas that filled a topographic depression in southeast elysium and then flowed into western amazonis planitia flow into western amazonis was facilitated by a series of channels carved by an earlier fluvial episode which were exploited by lavas as they moved down slope crater frequencies and stratigraphic relations indicate that the unit is very young upper amazonian the presence of such young flood lavas indicates 1 late in martian history large scale eruptions of low viscosity lava was still possible b sufficient heat remained in the mantle to mobilize large quantities of magma and c flood volcanism either continued or resumed in elysium after activity of the large central volcanoes had ceased each of these points are important considerations in understanding the martian thermal and volcanic history

modeling steam pressure under martian lava flows abstract rootless cones on mars are a valuable indicator of past interactions between lava and water however the details of the lava water interactions are not fully understood limiting the ability to use these features to infer new information about past water on mars we have developed a model for the pressurization of a dry layer of porous regolith by melting and boiling ground ice in the shallow subsurface this model builds on previous models of lava cooling and melting of subsurface ice we find that for reasonable regolith properties and ice depths of decimeters explosive pressures can be reached however the energy stored within such lags is insufficient to excavate thick flows unless they draw steam from a broader region than the local eruption site these results indicate that lag pressurization can drive rootless cone formation under favorable circumstances but in other instances molten fuel coolant interactions are probably required we use the model results to consider a range of scenarios for rootless cone formation in athabasca valles pressure buildup by melting and boiling ice under a desiccated lag is possible in some locations consistent with the expected distribution of ice implanted from atmospheric water vapor however it is uncertain whether such ice has existed in the vicinity of athabasca valles in recent history plausible alternative sources include surface snow or an aqueous flood shortly before the emplacement of the lava flow

radar sounding of temperate permafrost in alaska analogy to the martian midlatitude to high latitude ice rich terrains 1 radar detection of subsurface ice on mars has been widely debated in part because the dielectric signature of ice as deduced from the dielectric constant can be confused with dry silicate rich materials to identify the ice dielectric signature it is crucial to estimate the imaginary part of the dielectric permittivity inferred from the dielectric attenuation after removing the scattering loss unfortunately the latter remains poorly quantified at both mars advanced radar for subsurface and ionospheric sounding marsis and shallow subsurface radar sharad frequencies to address this ambiguity we conducted multiple frequency ground penetrating radar and resistivity investigations in well characterized temperate permafrost in fairbanks alaska the area shows several geomorphologic similarities to midlatitude and high latitude terrains on mars this approach allowed us to quantify the dielectric and scattering losses in temperate permafrost over the 10 to 1000 mhz frequency band at 20 mhz our results suggest an average dielectric loss rate of 0 25 0 03 db m whereas the corresponding average scattering loss rate is 0 94 0 37 db m the scattering loss was found to represent 69 of the total signal attenuation considering this result and the study by heggy et al 2006a in volcanic environments we revised the interpretation of the attenuation coefficient calculated from sharad data over the deuteronilus mensae region and amazonis planitia we then used the reevaluated dielectric loss to estimate the imaginary part of the dielectric permittivity our results suggest that even if deuteronilus mensae deposits and the vastitas borealis formation may have similar dielectric constants their imaginary parts are different this implies that the two regions have different bulk compositions with the former being ice rich sediments and the latter being nonconsolidated volcanic deposits

kilometer scale slopes on mars and their correlation with geologic units initial results from mars orbiter laser altimeter mola data martian surface slopes were calculated at baselines from 0 4 to 25 km using profiles obtained by the mars orbiter laser altimeter mola instrument during the aerobraking phase of the mars global surveyor mission median slope is proposed as a characteristic measurement of the typical surface roughness at each corresponding scale median slope is favored over rms slope because it is not influenced by the small number of higher slopes at the upper end of the slope frequency distribution tail median slope complements interquartile scale roughness characterization in that it is more sensitive to smaller baseline slopes a map of the median slope of the northern hemisphere is presented median slopes and their scale dependences are used to characterize typical kilometer scale roughness for a set of geologic units mapped in the northern hemisphere this analysis demonstrates that many individual units and groups of units are characterized by distinctive surface slopes and that these characteristics are sufficiently different that they hold promise for use in the definition and characterization of units characterization of the slope properties of geologic units provides information useful in the interpretation of their origin and evolution for example the generally smooth topography of the diverse vastitas borealis formation subunits is dominated by about 3 km 0 3 steep features almost indistinguishable in viking images the roughness characteristics of this unit differ from those of other geologic units on mars and suggest some distinctive process es of formation and or modification of kilometer scale topography common for all subunits the similarity of roughness characteristics of the several highland plateau units suggests that kilometer scale topography was largely inherited from the period of heavy bombardment the northern polar cap and layered terrains are largely very smooth at small scale the long steep sloped tails of the slope frequency distributions are compared for the dominant terrain types in the northern hemisphere of mars and are compared with earth continents the vastitas borealis formation found in the northern lowlands differs significantly from both cratered uplands and volcanic plains and these latter two units can be distinguished from each other on the basis of median slope terrestrial continents are smoother than cratered highlands but rougher than the vastitas borealis formation and most volcanic plains an inventory of all observed slopes much steeper than the angle of repose is presented steep slopes occur in the upper parts of tectonic scarps most likely representing bedrock exposures the presence of extremely steep slopes in the presumably ductile polar cap provides evidence for geologically recent and or ongoing formation of these slopes

geographic variations in the thermal and diffusive stability of ground ice on mars to investigate the stability of ground ice within the top several meters of the martian regolith time dependent models of the thermal and diffusive behavior of the regolith have been developed the geographic distribution of thermal inertia and albedo as well as the latitudinal variation in insolation have been included in calculations of surface and subsurface temperatures between 60 latitude ground ice was found to be stable where the annual mean surface and subsurface temperatures were below the atmospheric frost point this generally occurs poleward of the mid latitudes the latitude poleward of which ground ice is stable varies by about 20 to 30 from one longitude to another geographic variations in thermal inertia and albedo are the primary factors controlling regional variations in ice stability calculations of temperatures at high and low obliquity suggest that ground ice would be stable globally at high obliquity and would not be stable between 60 latitude at low obliquity thermally driven diffusion of atmospheric water vapor within the regolith was modeled accounting for both ordinary molecular and knudsen transport and equilibrium between ice vapor and adsorbed phases atmospheric water vapor was found to be able to supply the top few meters of the regolith with ice in regions where the annual mean surface temperature was below the atmospheric frost point ice was found to begin condensing in as short as 1000 martian years rapid accumulation of ice in the pore space of the upper layers of the regolith acted to choke transport to lower layers and slow the diffusion process even so after 105 martian years in some cases as much as 30 to 40 of the available pore space accumulated ice the total amount of subsurface ice ranged from a few to more than 25 g cm2 within the top few meters in regions of stability ground ice was found to form below a depth where the annual average vapor pressure over ice was equal to the annual average atmospheric vapor pressure near the surface atmospheric vapor was not found to accumulate as ice below a depth where the seasonal temperature oscillations gave way to the geothermal gradient the time scales for condensation of ground ice were found to be comparable to that of orbital oscillations suggesting that the present geographic distribution of ground ice may depend on the orbital history of mars

evidence for recent volcanism on mars from crater counts impact craters help characterize the age of a planetary surface because they accumulate with time they also provide useful constraints on the importance of surface erosion as such processes will preferentially remove the smaller craters earlier studies of martian crater populations revealed that erosion and dust deposition are important processes on mars they disagreed however on the age of the youngest volcanism these earlier studies were limited by image resolution to craters larger than a few hundred metres in diameter here we report an analysis using new images obtained by the mars global surveyor spacecraft of crater populations that extend the size distribution down to about 16 m our results indicate a wide range of surface ages with one region lava flows within the arsia mons caldera that we estimate to be no older than 40 100 million years we suggest that volcanism is a continuing process on mars

system of gigantic valleys northwest of tharsis mars latent catastrophic flooding northwest watershed and implications for northern plains ocean mars orbiter laser altimeter mola reveals a system of gigantic valleys to the northwest of the huge martian shield volcano arsia mons in the western hemisphere of mars these newly identified northwestern slope valleys nsvs potentially signify previously undocumented martian catastrophic floods and may corroborate the northern ocean hypotheses these features which generally correspond spatially to gravity lows were previously obscured in mariner and viking orbiter imagery by veneers of materials including volcanic lava flows and air fall deposits geologic investigations of the tharsis region suggest that the nsvs were mainly carved prior to the construction of arsia mons and its associated late hesperian and amazonian age lava flows concurrent with the early development of the outflow channels that debouch into chryse planitia

giant paleodictyon in eocene flysch abstract a giant paleodictyon gomezi with a maximum mesh diameter of 13 cm and covering more than 0 5 m2 occurs in the lower eocene flysch near zumaya the giant paleodictyon occurs with flute casts and therefore must have been produced deeply in the sediment the lengthening of mesh cells parallel and perpendicular to the flute casts implies changing current directions during trace production rows of elongate and offset mesh cells reflect the row by row production of the trace however the base line followed by the trace fossil producer meandering or spiral cannot be reconstructed because of incomplete preservation the extraordinary size of this giant paleodictyon contradicts the evolutionary trend of deep sea trace fossils toward optimization and miniaturization since similar large paleodictyon specimens occur in silurian flysch

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

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

a new survey of multiring impact basins on mars multiring impact basins have profoundly influenced the geologic evolution of mars we compile and summarize the evidence for martian impact basins and suggest eight new examples multiring basins on mars define three morphologic subclasses with increasing basin size basins having diameters 300 3600 km have extremely shallow topographic profiles and numerous concentric structures expressed as scarps massifs and channels radial and concentric structures analogous to those associated with orientale are not apparent for basins of argyre size or larger these variations in basin morphology and structure may be associated with mechanical interactions between basin forming impacts relatively thin weak lithosphere and for the largest impacts spherical target geometry multiring basins are recognized on all parts of mars including tharsis elysium and the northern lowlands much of the subsequent resurfacing of cratered terrain such as lunae planum ridged plains is associated spatially with multiring basins nucleation of long lived volcanic complexes in tharsis and elysium was probably aided by early impact basins the planetary terrain dichotomy was probably established during the period of heavy meteoritic bombardment and subsequent processes in the northern plains region were not sufficiently vigorous to destroy or completely obscure the underlying multiring basin fabric the revised population of multiring basins is consistent with the size frequency distribution of craters 500 km in diameter on mars basins having diameters 500 d 1850 km are characterized by a cumulative frequency slope of 0 75 0 16 whereas the larger basins define a slope of 1 7 0 45 this change in slope occurs over the same diameter range as the significant change from orientale type basin morphology at smaller diameters to argyre and chryse type basin morphology the population of craters and basins on mars confirms that the relative crater densities on the terrestrial planets due to heavy bombardment are comparable perhaps suggesting a common source for the impacting objects

the gravity field of mars results from mars global surveyor observations of the gravity field of mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes the rough elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near isostatic compensation whereas the smooth low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south the northern hemisphere shows evidence for buried impact basins although none large enough to explain the hemispheric elevation difference the gravitational potential signature of tharsis is approximately axisymmetric and contains the tharsis montes but not the olympus mons or alba patera volcanoes the gravity signature of valles marineris extends into chryse and provides an estimate of material removed by early fluvial activity

grjota valles and implications for flood sediment deposition on mars 1 grjota valles is one of mars four amazonian aged fissure headed catastrophic flood channels it originates at the northwestern most cerberus fossa and stretches several hundred kilometers eastward and southward moats around in channel knobs and various small scale mounds similar to mounds seen in athabasca valles are both attributed to flood related processes the floodwater sinks are ambiguous and the lack of recognizable flood deposits is attributed to two causes the first cause is the channel s high width to depth ratio which may have facilitated floodwater recession during flooding the second cause is the tendency of floodwater under lower gravity to move a higher percentage of material as washload as flood deposits are comprised of bedload and suspended load this tendency would result in fewer depositional bedforms our analysis of grjota valles supports the idea that formation of terrestrial style flood deposits is energetically unlikely on mars and that their presence indicates special paleohydraulic conditions

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars 1 amazonis planitia located between the two main volcanic provinces on mars tharsis and elysium is characterized by extremely smooth topography at several scale lengths as smooth as oceanic abyssal plains topography on earth we use mars global surveyor mgs data primarily very high resolution mars orbiter laser altimeter mola topography and derivative slope maps gradient maps and detrended maps to examine the surface morphology of amazonis planitia and the stratigraphic relationships among previously mapped and newly defined units these new data reveal the presence of a 1300 km diameter noachian impact basin in northwest amazonis planitia and an extensive late hesperian lava flow unit that appears to have originated from the olympus mons source area prior to aureole formation the presence of this previously unrecognized flow unit strongly suggests that olympus mons activity dates back to at least the hesperian as did activity on the tharsis montes emplacement of this 100 meter thick flow unit formed a barrier along the northern margin of amazonis planitia which had a profound influence on the subsequent geologic history of the region formation of olympus mons aureole deposits created an eastern topographic barrier and subsequent tharsis montes lava flows entered the basin from the south flowing around the aureole these three barriers degraded noachian crater rim protoolympus mons flow unit and olympus mons aureole caused subsequent lava flows and outflow channel effluents primarily from the elysium region to the west to pond on the floor of amazonis planitia preferentially smoothing the terrain there mars orbiter camera moc images substantiate that at least two very fluid lava flows alternated with fluvial episodes from elysium planitia flowing through marte valles onto the floor of the amazonis planitia basin within amazonis planitia moc images show flow like textures heavily mantled by sediments and radar data reveal the presence of rough lava flow surfaces underlying the sedimentary debris these data thus suggest that the unique smoothness of amazonis planitia is the result of deposition of thin fluid lava flows and fluvial sediments in an enclosed basin crater counts suggest that the most recent resurfacing may have occurred in the latest amazonian period in the last 1 of the history of mars in light of its unique history it is somewhat ironic to note that amazonis planitia was originally thought to be a typical young martian surface and therefore used to name the amazonian era index terms 6225 planetology solar system objects mars 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5480 planetology solid surface planets volcanism 8450 4267 oceanography general paleoceanography keywords mars water amazonis planitia marte vallis volcanism amazonian citation fuller e r and j w head iii amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars j geophys res 107 e10 5081 doi 10 1029 2002je001842 2002

topography roughness layering and slope properties of the medusae fossae formation from mars orbiter laser altimeter mola and mars orbiter camera moc data the enigmatic medusae fossae formation mff is one of the youngest surficial deposits on mars previously proposed modes of origin include pyroclastic volcanism eolian mantling polar sedimentation carbonate platform and paleoshorelines in order to assess mapped member boundaries and constrain likely origin processes we analyze five topographic transects from the mars orbiter laser altimeter mola collected during the aerobraking hiatus orbit period of the mars global surveyor mgs mission together with several simultaneously acquired mars orbiter camera moc images to examine the regional and local variations in the relief slopes vertical roughness and relative elevations of mapped mff members we find that the members are not particularly flat or level but have average thicknesses of many hundreds of meters and substantially more internal relief than previously thought locally the mff members are sometimes distinguishable by slope elevation and surface roughness characteristics but no unique formation wide characteristics are apparent in this analysis of the limited initial data the relative elevations of the mapped members are not consistent with undeformed planar horizontal layers but may be consistent with layers draped over preexisting topography with subsequent partial removal analysis of the initial coincident moc and mola hiatus data suggests the possible presence of local layers as well as the mislocation of at least a few mff member and formation boundaries we conclude that carbonate and shoreline deposit origins are not as well supported in the initial mgs data as they were in the viking data and that the mff formation and member boundaries should be reexamined in conjunction with the incoming new mgs data

mars northern hemisphere slopes and slope distributions we investigate slope distributions in the northern hemisphere of mars from topographic profiles collected by the mars orbiter laser altimeter analysis of the region from about 12 s to 82 n over diverse geologic units indicates that the range of regional scale slopes is small generally 3 surface smoothness is most distinctive in the vast northern hemisphere plains where slopes are typically 1 amazonis planitia is particularly remarkable in its smoothness exhibiting an rms variation in topography of 2 m over a 100 km baseline this relative smoothness is still present when compared with other sampled areas of the martian northern hemisphere and with volcanically resurfaced terrains elsewhere in the solar system planetary surfaces of large areal extent that are most comparable to amazonis in terms of rms elevation variation over long baselines are depositional in origin and include terrestrial oceanic abyssal plains and certain sedimentary basins slopes across the valles marineris canyon system show that the upper portion of the walls are significantly and consistently steeper than the lower walls characteristic of extensive mass wasting the observed long runout is consistent with a high energy collapsed flow in the neighboring noctis labyrinthus canyons the duality between the upper and lower walls is reduced and indicates a lower energy modificational history and or greater cohesion of wall rock

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

overview of the mars global surveyor mission the mars global surveyor spacecraft was placed into mars orbit on september 11 1997 and by march 9 1999 had slowly circularized through aerobraking to a sun synchronous near polar orbit with an average altitude of 378 km the science payload includes the mars orbiter camera mars orbiter laser altimeter thermal emission spectrometer ultrastable oscillator for radio science experiments and magnetometer electron reflectometer package in addition the spacecraft accelerometers and horizon sensors were used to study atmospheric dynamics during aerobraking observations are processed to standard products by the instrument teams and released as documented archive volumes on 6 month centers by the planetary data system significant results have been obtained from observations of the interior surface and atmosphere for example mars does not now have an active magnetic field although strong remanent magnetization features exist in the ancient crust these results imply that an internal dynamo ceased operation early in geologic time altimetry and gravity data indicate that the crust is thickest under the south pole thinning northward from the cratered terrain to the northern plains analysis of altimetry data demonstrates that mars is egg shaped with gravitational equipotential contours that show that channel systems in the southern highlands drained to the north largely to the chryse trough a closed contour in the northern plains is consistent with the existence of a great northern ocean emission spectra of low albedo regions show that basaltic rocks dominate spectral signatures on the southern highlands whereas basaltic andesites dominate the northern lowlands the bright regions show nondiagnostic spectra similar to that of dust in the atmosphere signatures of aqueous minerals e g clays carbonates and sulfates are noticeably absent from the emission spectra high spatial resolution images show that the surface has been extensively modified by wind and that layering is nearly ubiquitous implying that a complex history of events is recorded in surface and near surface materials altimetry data imply that both permanent caps are composed of water ice and dust with seasonal covers of carbon dioxide frost finally the altimetry data coupled with thousands of atmospheric profiles are providing new boundary conditions and dynamic controls for the generation and testing of more realistic dynamic models of the global circulation of the atmosphere

last glacial maximum climate in new zealand inferred from a modelled southern alps icefield abstract we present a simulation of the new zealand southern alps icefield at the last glacial maximum lgm c 30 000 20 000 calendar years ago ka in an attempt to constrain the climate of that period we use a 500 m resolution ice sheet model parameterised using empirical glaciological climatological and geological data specific to the model domain to simulate the entire southern alps icefield we find that an lgm cooling of at least 6 6 5 c is necessary to bring about valley glaciers that extend beyond the mountains however climate topography thresholds related to the elevation and hypsometry of individual catchments control the gradient of the rate of glacier expansion in the domain and in order to remain within geologically reconstructed lgm limits we find that the lgm cooling was most likely associated with a precipitation regime up to 25 drier than today wetter than present scenarios give rise to equilibrium line depressions and ice extents that are incompatible with empirical evidence these results perhaps indicate that either the westerly air masses affecting new zealand during the lgm were drier than today or that they were weaker or zonally displaced with respect to present

an altitude normalized magnetic map of mars and its interpretation techniques developed for the reduction and analysisofterrestrialsatellitemagneticelddataareusedto better understand the magnetic eld observations made by mars global surveyor a global distribution of radial br magnetic eld observations and associated uncertainties is invertedfor an equivalentsource magnetization distribution and then used to generate an altitude normalized map of br at 200 km the observations are well represented by a potential function of crustal origin consistent with a rema nent origin for the martian magnetic features the correla tion between the 40546 br observations andbr calculated from the magnetization solution at observation locations is 0 978 for a magnetization distribution connedto a 50 km layer calculatedmagnetizationsrangefrom 22to 17a m we see correlations with tectonics that were only hinted at in earlier maps magnetic features appear to be truncated against valles marineris and ganges chasma suggestive of a major change in crustal properties associated with fault ing

evidence for remnants of ancient ice rich deposits mangala valles outflow channel mars high resolution spacecraft data reveal the presence of a distinctive unit on the upper reaches of the floor of mangala valles an ancient outflow channel on mars in contrast to abundant evidence for scour intense erosion and hydrodynamic shaping typical of the floors and margins of mangala and other outflow channels this unit is smooth surfaced has cuspate margins is superposed on the scoured valley floor and is extensively pitted we interpret this unit to be the sublimation lag deposit derived from an ice thermal boundary layer on the aqueous flood that formed the outflow channel system and the remnant of floodwaters trapped in channel lows this interpretation further supports the likelihood that climate conditions at the time of emplacement were similar to the hyper arid cold desert conditions of today frozen floodwaters from the ancient martian subsurface could still be preserved in these deposits representing attractive and accessible exobiological exploration objectives

piaeodicton the traces of infaunal xenophyophores a xenophyophore found just below the surface of a box core of modern deep sea sediment from the japan trench has a threadlike plasma body that extends through horizontal anastomosing networks of organically bound sediment tubes the organism s test the tubes resemble somne of the polygonal networks of the trace fossil paleodictyon such xenophyophores may be the makers of paleodictyon and the complex regular geometry of paleodictyon may be determined by the xenophyophore s anastomosing body shape

lava water interaction and hydrothermal activity within the 2014 2015 holuhraun lava flow field iceland abstract lava that erupted during the 2014 2015 holuhraun eruption in iceland flowed into a proglacial river system resulting in aqueous cooling of the lava and an ephemeral hydrothermal system we carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time using thermocouple measurements and data logging sensors the heat loss rate from advection through this hydrothermal system in august 2015 was 5 5 108 w since eruption aqueous cooling likely accounted for 1 of the total heat loss from the lava this estimate excludes steam losses from fumaroles as well as any groundwater that was not released to the surface and thus is a lower bound near the terminus of the flow advection of heat by flowing water may have locally accounted for tens of percent of the total cooling of that part of the flow our data quantify the importance of water cooling for this lava flow and can be compared with models to better understand lava water interactions more generally we also provide detailed methods for simple low cost monitoring of similar instances in the future

state of stress faulting and eruption characteristics of large volcanoes on mars the formation of a large volcano loads the underlying lithospheric plate and can lead to lithospheric flexure and faulting in turn lithospheric deformation affects the stress field beneath and within the volcanic edifice and can influence magma transport modeling the interaction of these processes is crucial to an understanding of the history of eruption characteristics and tectonic deformation of large volcanoes we develop models of time dependent stress and deformation for the tharsis volcanoes on mars by means of a finite element code we calculate stresses and displacements due to a volcano shaped load emplaced on an elastic plate overlying a viscoelastic mantle models variously incorporate growth of the volcanic load with time and a detachment between volcano and lithosphere the models illustrate the manner in which time dependent stresses induced by lithospheric plate flexure beneath the volcanic load may affect eruption histories and the derived stress fields can be related to tectonic features on and surrounding martian volcanoes as a result of flexure there are three regions where stresses become sufficiently large to cause failure by faulting according to the mohr coulomb criterion at the surface of the plate just outward of the volcano near the base of the elastic lithosphere beneath the center of the volcano and on the upper flanks of the volcano early in its growth history normal faulting is the dominant mode of failure predicted for the first region consistent with circumferential graben observed around the tharsis montes and with the scarp at the base of olympus mons interpreted as a large offset listric normal fault normal faulting mostly radially oriented is predicted for the second region failure in the third region is predicted to consist of thrust faulting circumferentially oriented on the upper and middle flanks and radially oriented on the lower flanks in models simulating a growing volcano this portion of the edifice is subsequently covered by later units which exhibit lower stresses and are not predicted to fail this volume of early failure remains the most highly stressed area in the edifice concentric terraces interpreted by some workers as thrust faults on the upper flanks of olympus mons may correspond to the predicted circumferential thrust features if the most recent increments of volcano growth were relatively large or in the presence of local material property or stress field variations for volcanoes detached from the plate predicted failure in the edifice takes the form of radial normal faulting near the volcano base the addition of a local extensional stress arising from the regional topographic slope yields a pattern of predicted faulting which closely matches that observed on the tharsis montes including the development of radial rifts on the lower volcano flanks to the northeast and southwest and the asymmetric formation of circumferential flank graben this stress state is also consistent with an interpretation of the aureole deposits of olympus mons as the result of gravity sliding along a basal detachment our models also suggest an explanation for the lack of strike slip features predicted by previously published flexural models around the tharsis volcanoes for a given load increment the first mode of near surface failure for most of the area immediately outward of the load is circumferential normal faulting and graben formation as the volcano grows and the flexural response to the increasing load proceeds the predicted failure mode in a portion of this annular region surrounding the volcano changes to strike slip faulting because normal faulting has been predicted to have taken place earlier however it is likely that release of later stresses will occur by reactivation and growth of these normal faults and graben rather than by the formation of new strike slip faults

structural evolution of the northern cerberus fossae graben system elysium planitia mars to determine whether the structural evolution of the northern cerberus fossae ncf was dominated by cryospheric melting and collapse or fault related subsidence we used moc themis and hirise images and mola data to document spatial variations in vertical offset along strike the fossae are a series of fractures on the martian surface that cross cut noachian hesperian and in places very young late amazonian terrain serial cross sections across the fracture related topography from mola data show that vertical offsets are not greater where fractures traverse older terrain showing that offsets have accumulated since the formation of the amazonian terrain vertical offsets are greater in the central portions of the fracture system with the profile resembling that for a single fault system topographic features that pre date deformation are preserved on the graben floors suggesting little sediment infill so the mola elevation measurements constrain total vertical offsets since the fractures formed deficits in vertical offset occur where fractures have not linked and remain en echelon across relay zones or have linked leaving palaeo graben tips this indicates that the traces of the fractures propagate along strike at the surface and intersect over time periods that are likely to be in the range of 105 106 years rather than in a single collapse event deficits are also in places associated with collapse pits suggesting such collapse is the early stage of graben subsidence at propagating lateral graben tips we use these observations to argue that the primary mechanism causing subsidence is not cryospheric melting and collapse but faulting

paleodictyon nodosum a living fossil on the deep sea floor we report new in situ observations and laboratory studies of specimens of a small diameter 2 4 7 5 cm strikingly hexagonal form originally described from sedimented steps in a wall of the axial valley of the mid atlantic ridge water depth 3430 3575 m near 26 n 45 w that appears to be identical to the iconic form paleodictyon nodosum described as a trace fossil from eocene flysch deposits at sites in europe and wales our findings follow the form is apparently agglutinated in sea floor sediment a veneer of calcareous lutite over red metalliferous sediment and consists of three equidistant rows of tiny holes diameter 1 mm that intersect at an angle of 120 and continuously connect through vertical shafts length 2 3 mm with an underlying horizontal network of tubes or tunnels identical with the fossil form the number of rows of holes and spacing of rows increase with overall diameter of the form indicative of organic growth the form is shaped like a shield surrounded by a lip and moat with surface relief 0 5 cm that is absent in the fossil form the surface relief exposes the underlying red sediment and may have been produced either by excavation constructional origin or by infaunal growth body form protoplasm is absent in recovered specimens as indicated by negative results of staining techniques explained by either initial absence or loss genetic sequencing of material from the form identified different foraminifera that had settled on the pattern of holes which acts as a baffle to trap organic matter models in flume tanks show that the shield like form deflects flow of ocean currents into a self ventilating structure capable of aerating and of circulating organic particles through the tubes or tunnels microbial counting techniques indicated background abundances within and outside the form we come to two alternative interpretations of the findings resolvable with further studies the modern p nodosum is a burrow consistent with interpretation of the ancient form as a trace fossil the modern p nodosum is a compressed form of a hexactinellid sponge adapted to a sedimentary substrate which means that the ancient form is a body fossil with possible affinity to the ediacara fauna

long term wind erosion on mars abstract wind erosion and deposition are powerful agents of surface change on mars erosion is sensitive to the atmospheric density so feedback between orbit variations and atmospheric density can enhance the sensitivity of erosion rates to orbital parameters we use statistics derived from a 1 gyr integration of the spin axis of mars coupled with runs of the nasa ames 3 d general circulation model gcm at a variety of orbital conditions and pressures to explore this feedback we find that wind erosion in the gcm is associated with two factors baroclinic zone winds and strong cross equator solstice flows both of these factors are influenced by topography producing an asymmetry in the erosion pattern between the north and the south the erosion model averaged over 1 gyr produces potential erosion rates of 1 7 10 5 m yr 1 in the north and 1 0 10 5 m yr 1 in the south which increase by an order of magnitude in an early 28 mbar atmosphere the stability of these potential erosion patterns over geological time indicates that the lowland regions of mars are continuously eroded and that wind is capable of revealing ancient sedimentary deposits or eroding substantial deposits that may have otherwise been preserved

rootless cones on mars indicating the presence of shallow equatorial ground ice in recent times high resolution mars orbiter camera moc images have revealed the existence of clusters of small cones in the cerberus plains marte valles and amazonis planitia mars these cones are similar in both morphology and planar dimensions to the larger of icelandic rootless cones which form due to explosive interactions between surficial lavas and near surface groundwater impact crater size frequency relationships indicate that surfaces upon which the cones sit are no older than 10 ma if martian cones form in the same manner as terrestrial rootless cones then equatorial ground ice or ground water must have been present near the surface in geologically recent times

crater geometry and ejecta thickness of the martian impact crater tooting we use mars orbiter laser altimeter mola topographic data and thermal emission imaging system themis visible vis images to study the cavity and the ejecta blanket of a very fresh martian impact crater 29 km in diameter with the provisional international astronomical union iau name tooting crater this crater is very young as demonstrated by the large depth diameter ratio 0 065 impact melt preserved on the walls and floor an extensive secondary crater field and only 13 superposed impact craters all 54 to 234 meters in diameter on the 8120 km 2 ejecta blanket because the pre impact terrain was essentially flat we can measure the volume of the crater cavity and ejecta deposits tooting crater has a rim height that has 500 m variation around the rim crest and a very large central peak 1052 m high and 9 km wide crater cavity volume i e volume below the pre impact terrain is 380 km 3 and the volume of materials above the pre impact terrain is 425 km 3 the ejecta thickness is often very thin 20 m throughout much of the ejecta blanket there is a pronounced asymmetry in the ejecta blanket suggestive of an oblique impact which has resulted in up to 100 m of additional ejecta thickness being deposited down range compared to the up range value at the same radial distance from the rim crest distal ramparts are 60 to 125 m high comparable to the heights of ramparts measured at other multi layered ejecta craters tooting crater serves as a fresh end member for the large impact craters on mars formed in volcanic materials and as such may be useful for comparison to fresh craters in other target materials

statistics of mars topography from the mars orbiter laser altimeter slopes correlations and physical models data obtained recently by the mars orbiter laser altimeter mola were used to study the statistical properties of the topography and slopes on mars we find that the hemispheric dichotomy manifested as an elevation difference can be described by long baseline tilts but in places is expressed as steeper slopes the bimodal hypsometry of elevations on mars becomes unimodal when referenced to the center of figure contrary to the earth for which the bimodality is retained however ruling out a model in which the elevation difference is expressed in a narrow equatorial topographic step cannot be done by the hypsometry alone mars slope distribution is longer tailed than those of earth and venus indicating a lower efficiency of planation processes relative to relief building tectonics and volcanics we define and compute global maps of statistical estimators including the interquartile scale rms and median slope and characteristic decorrelation length of the surface a correspondence between these parameters and geologic units on mars is inferred surface smoothness is distinctive in the vast northern hemisphere plains where slopes are typically 0 5 amazonis planitia exhibits a variation in topography of 1 m over 35 km baselines the region of hematite mineralization in sinus meridiani is also smooth with median slopes lower than 0 4 but does not form a closed basin the shallower long wavelength portion of the lowlands topographic power spectrum relative to the highlands can be accounted for by a simple model of sedimentation such as might be expected at an ocean s floor the addition of another process such as cratering is necessary to explain the spectral slope in short wavelengths among their application these mola derived roughness measurements can help characterize sites for landing missions

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

quantitative ichnology of modern pelagic deposits in the abyssal atlantic abstract quantitative sedimentologic aspects of bioturbation were investigated in a series of deep sea box cores which were collected over a broad latitudinal range 35 n to 30 s and bathymetric range 1 4 to 5 7 km in the central atlantic ocean all cores were thoroughly bioturbated and numerous generations of burrowing could be discerned in many instances preservation of individually distinct burrows ranged from poor to excellent and eight ichnogenera plus several unnamed biogenic structures were recognized the distribution of calcium carbonate organic carbon selected species of planktic foraminifera and sediment grain size were examined in several cores these measurements indicated that the surficial mixed layer which ranged from 3 to 10 cm thick was statistically more homogeneous than the underlying transition layer this relationship is seen most clearly with respect to lateral and vertical variations in the calcium carbonate content of the cores bioturbation of abyssal pelagic deposits appears to be a two phase process consisting of a homogenization of the upper few centimeters i e the mixed layer by shallow burrowing meiofauna and b heterogeneous mixing of the underlying strata i e the transition layer by relatively deep burrowers the heterogeneously mixed transition layer becomes the preserved trace fossil record under normal circumstances the homogenized mixed layer is not preserved

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

the olympus mons aureole formation by gravitational spreading new observations of the aureole deposits of olympus mons are in agreement with previous suggestions that the aureole lobes could have been formed by movement under gravity away from the observed scarps the characteristic corrugated morphology of the aureole is probably secondary formed by erosion along structural inhomogeneities geometries of the corrugations and translational faults in the aureole deposits favor a mechanism of emplacement that involves material with substantial shear strength rather than viscous flow estimates of the aspect ratios of terrestrial landslides nappes and ash flows suggest that the aureole deposits are more similar in overall shape to slide emplaced bodies than to pyroclastic flows although martian physical conditions permit the formation of ash flows there is no positive evidence for their existence a gravitational spreading mechanism is proposed that involves imbricate thrusting in distal regions analogous with terrestrial thrust sheets corrugations in the aureole developed by erosion along imbricate or listric faults basal shear stresses on the decoupling surface may have been of the order of 106 pa 10 bars the nature of the decoupling surfaces in the proximal regions is uncertain but is likely to have been the topographic surface in distal parts the aureole deposits were probably emplaced as a series of sheets by spreading under gravity from an ancestral olympus mons which extended farther to the northwest than does the present volcano as a result of the accumulation of lavas under the then prevailing stress conditions recent lava eruptions from the volcano have been concentrated in northeast and southwest sectors indicating a changed stress regime since aureole emplacement

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

inverted fluvial features in the aeolis zephyria plana western medusae fossae formation mars evidence for post formation modification 1 the aeolis and zephyria plana contain the western most portion of the medusae fossae formation mff an enigmatic and extensive light toned deposit located in the martian equatorial region and dated from the hesperian to amazonian epochs this area hosts a large population of sinuous ridges srs interpreted as inverted fluvial features formed by precipitation indurated by chemical cementation buried by subsequent deposition and finally exhumed this interpretation of srs as uniformly fluvial represents a modification to an earlier hypothesis for one particular sr of possible glaciofluvial i e esker formation these srs provide a tool to investigate the degree and character of post fluvial modification processes in this region we combined digital terrain models made from context camera ctx and high resolution imaging science experiment hirise stereo image pairs with individual data points from the mars orbiter laser altimeter mola to estimate relief cross sectional profiles longitudinal profiles and slope directions of selected srs longitudinal profiles of several srs display undulations with amplitudes of up to order 100 m while some of the lower amplitude undulations may be due to differential erosion undulations having amplitudes in excess of sr relief require alternative explanations our combined morphologic and topographic analysis suggests that multiple post flow processes including compaction of the deposits and tectonic displacements have modified the original sr profiles specification of the type s and magnitudes of these modification processes will contribute to understanding both the potential of post flow modification of fluvial profiles elsewhere on mars as well as the nature and properties of the mff