viscous flow features on the surface of mars observations from high resolution mars orbiter camera moc images 10 5 10 7 years of the material our shear stress estimates of 10 1 5 10 2 5 mpa yield strain rates on the order of 10 11 10 16 s 1 which are within the superplastic flow regime of ice mean annual surface temperatures age constraints and strain estimates show that it is possible for a meters thick ice dust mixture to undergo viscous deformation under past or present surface conditions for ice grain sizes 10 mm the meters thick layer in which the viscous flow features formed is morphologically similar to a degraded meters thick ice dust surface deposit dissected mantle terrain locations of the viscous flow features dissected mantle terrain and recent gullies are concentrated in the midlatitude regions and all three show identical distributions as a function of latitude with the maximum frequency of occurrence at 40 n and s the strong association between these small scale flow features and the dissected mantle terrain large scale viscous flow features and recent gullies imply that deposition deformation and removal of ice rich materials has played an important role in the modification of the surface in the midlatitudes of mars during the amazonian and possibly longer index terms 5470 planetology solid surface planets surface materials and properties 5416 planetology solid surface planets glaciation 1863 hydrology snow and ice 1827 1823 hydrology frozen ground 8168 tectonophysics stresses general keywords viscous flow viscous creep dissected mantle terrain ice rich deposits mars climate recent gullies

the importance of secondary cratering to age constraints on planetary surfaces small craters less than one kilometer diameter can be primary craters produced by impact of interplanetary debris or they can be secondary craters produced by fallback of high velocity ejecta blocks from much larger but infrequent primary impacts the prevalent assumption over recent decades has been that primaries are most abundant so most small craters are independent random events and can be used for dating however recent results from europa and mars support the early theory that distant secondaries globally dominate the number of small lunar craters this would invalidate part of production functions that have been widely used for age dating crater excavation results in higher mean ejection velocities for smaller fragments resulting in a steeper size frequency distribution for secondary craters than is produced by the same size frequency distribution of interplanetary debris this review also discusses how small craters can sometimes be used to derive meaningful age constraints

the landscape of titan as witness to its climate evolution we investigated the range of titan climate evolution hypotheses regulated by the role sources and availability of methane we analyzed all available image data principally synthetic aperture radar sar of titan s landscape through the t 86 encounter starting with focused examinations of terrains that carry the markers of climate evolution traditional geologic and geomorphic landscape analysis was used to perform morphometric characterization establish time stratigraphic relationships and interpret local and regional geologic process oriented evolutionary histories we then assayed the distribution of terrains we identified with respect to both their latitudinal and altimetric occurrence our analysis of the terrain types and distributions was used to evaluate and rank the various climate evolution scenarios we favor progressive hypotheses which include a relatively brief period in which precipitation was able to affect geomorphic change in low latitudes at scales perceivable in sar data with subsequent gradual decline of precipitation intensity coupled with an increasing poleward restriction

soft sediment deformation in upper proterozoic torridonian sandstones applecross formation at torridon northwest scotland abstract the applecross formation upper proterozoic torridon group northwest scotland was deposited as planar laminated and cross bedded coarse sands in braided streams soft sediment deformation is described from a 97 m thick study section most of which comprises contorted stratification the main structures are cusps and complex recumbent folded cross bedding formed by water escape during fluidization four assemblages of structures are recognized deformation as isolated structures in an otherwise undeformed unit may have been triggered by fluid turbulence discrete and chaotic units record widespread liquefaction and fluidization respectively of the most recently deposited sediment deformation may have been triggered by upwelling groundwater multilayer complexes formed when water escape from a buried layer generated fluidization in the overlying sediment this may have been triggered by seismically induced liquefaction some parts of the succession were disturbed on separate occasions by different processes sediment laden currents are unlikely to have been a major trigger for deformation it is concluded that specific soft sediment deformation structures result from the combination of driving forces deformation mechanism and initial geometry assemblages of structures relate to the timing of deformation and are of more value in identifying the trigger for deformation

possible long term decline in impact rates 1 martian geological data abstract quantin et al quantin c allemand p mangold n delacourt c 2004a icarus 172 555 572 tabulated crater count data for 56 landslides along the walls of valles marineris under the assumption of a constant cratering rate after about 3 gyr ago as used in the 1999 2005 iterations of the crater chronology isochron system of hartmann and in the hartmann and neukum system these data indicate a regularly increasing rate of landslides which would be difficult to explain we suggest that these data may support a decline in inner solar system cratering rates by about a factor of 3 since 3 gyr ago not unlike predictions based on asteroid belt collision models such a decline is also supported by our review of data on lunar impact melts and glass spherules in a companion paper hartmann w k quantin c mangold n 2007 icarus 186 11 23 such models produce not only a more uniform rate of landslides over the last 3 gyr but also a more uniform rate of resurfacing processes which also had an apparent increase under the assumption of a constant cratering rate

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

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

hellas planitia mars site of net dust erosion and implications for the nature of basin floor deposits hellas planitia located within an enclosed basin which includes the lowest topography on mars appears to be undergoing net erosion dust is removed from the basin it probably contributes to global dust storms and should leave behind a coarse lag the particle size distributions and particularly the rock or boulder populations in this lag might be useful for distinguishing between processes which formed the lithologic units that comprise hellas planitia this report concludes that the abundance of rock particles larger than coarse sand is very low although this hypothesis awaits confirmation from forthcoming spacecraft data the origins for hellas floor deposits favored by this study are indurated volcanic airfall or ancient loess lacustrine deposits and some types of volcanic mud flows the conclusions of this study tend to disfavor such geologic processes as blocky lava flows glacial deposits e g moraines or boulder laden catastrophic flood outwash

characterization of hydrated silicate bearing outcrops in tyrrhena terra mars implications to the alteration history of mars abstract the tyrrhena terra region of mars is studied with the imaging spectrometers omega observatoire pour la mineralogie l eau les glaces et l activite onboard mars express and crism compact reconnaissance infrared spectrometer for mars onboard mars reconnaissance orbiter through the observation of tens of craters that impacted into this part of the martian highlands the 175 detections of hydrated silicates are reported mainly associated with ejecta blankets crater walls and rims and central up lifts sizes of craters where hydrated silicates are detected are highly variable diameters range from less than 1 km to 42 km we report the presence of zeolites and phyllosilicates like prehnite mg chlorite mg rich smectites and mixed layer chlorites smectites and chlorite vermiculite from comparison of hyperspectral infrared observations with laboratory spectra these minerals are associated with fresh craters post dating any aqueous activity they likely represent ancient hydrated terrains excavated by the crater forming impacts and hence reveal the composition of the altered noachian crust although crater related hydrothermal activity may have played a minor role for the largest craters 20 km in diameter most detected minerals formed over relatively high temperatures 100 300 c likely due to aqueous alteration of the noachian crust by regional low grade metamorphism from the noachian thermal gradient and or by extended hydrothermal systems associated with noachian volcanism and ancient large impact craters this is in contrast with some other phyllosilicate bearing regions like mawrth vallis where smectites kaolinites and hydrated silica were mainly identified pointing to a predominance of surface shallow sub surface alteration and where excavation by impacts played only a minor role smooth plains containing hydrated silicates are observed at the boundary between the noachian altered crust dissected by fluvial valleys and the hesperian unaltered volcanic plains these plains may correspond to alluvial deposition of eroded material the highlands of tyrrhena terra are therefore particularly well suited for investigating the diversity of hydrated minerals in ancient martian terrains

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

hirise views enigmatic deposits in the sirenum fossae region of mars hirise images together with other recent orbital data from mars define new characteristics of enigmatic hesperian aged deposits in sirenum fossae that are mostly 100 200 m thick drape kilometers of relief and often display generally low relief surfaces new characteristics of the deposits previously mapped as the electris deposits include local detection of meter scale beds that show truncating relationships a generally light toned nature and a variably blocky weakly indurated appearance boulders shed by erosion of the deposits are readily broken down and contribute little to talus thermal inertia values for the deposits are 200 j m 2 k 1 s 1 2 and they may incorporate hydrated minerals derived from weathering of basalt the deposits do not contain anomalous amounts of water or water ice deflation may dominate degradation of the deposits over time and points to an inventory of fine grained sediment together with constraints imposed by the regional setting on formation processes these newly resolved characteristics are most consistent with an eolian origin as a loess like deposit comprised of redistributed and somewhat altered volcanic ash constituent sediments may be derived from airfall ash deposits in the tharsis region an origin directly related to airfall ash or similar volcanic materials is less probable and emplacement by alluvial fluvial impact lacustrine or relict polar processes is even less likely

carving intracrater layered deposits with wind on mars crater basins on mars host thick sedimentary sequences which record the environments of early mars these basin fills commonly exhibit mound morphologies thought to arise from aeolian erosion of initially crater filling strata this study presents transport based models explaining how mounds could be carved by wind wind tunnel experiments generated morphologies similar to those observed on mars and numerical modeling of flow over a crater using large eddy simulation les demonstrated a positive feedback between topographic focusing of flow and erosion potential observations of yardangs dunes and wind streaks all proxies for wind direction largely agree with model results where mound strata origins have been interpreted basal subaqueous deposits are overlain by aeolian deposits this stratigraphic progression culminating in wind driven excavation is consistent with a global desiccation event the occurrence of sedimentary mounds only on noachian terrain argues that this event was related to late noachian climatic change

on the implementation of passive open boundary conditions for a general circulation model the barotropic mode the objective of this study is to evaluate the performance of several open boundary conditions applied to the princeton ocean model the focus is on passive open boundary conditions applied to the external mode i e conditions that are applied when the mean flow at the open boundary is unknown and the values of the variables must be assumed or extrapolated from the interior solution three types of open boundary conditions obcs are tested 1 radiation conditions 2 characteristic methods 3 relaxation schemes numerical experiments are conducted in a zonal channel that include different forms of bottom topography the experiments are designed to emphasize flow conditions dominated by direct wind forcing or wave radiation three sets of experiments are discussed 1 forcing by a uniform alongshelf wind stress 2 the barotropic adjustment of an initial perturbation in the sea surface elevation and 3 forcing by a traveling storm the results of these experiments are compared with analytical solutions and the results of experiments using cyclic boundary conditions or expanded domains according to our results all radiation schemes of orlanski s type perform poorly in either flows with strong nonlinear components or when the model response is dominated by the propagation of dispersive wave packets the characteristic method recommended by roed and cooper 1987 provided reasonable responses in most cases but we found problems in handling dispersive waves or variable wind forcing at the open boundaries although there were limitations in all the obcs that we tested the best overall performances were for the conditions proposed by flather 1976 combined with a local solution approach proposed by roed and smesdtad 1984 and the flow relaxation scheme developed by martinsen and engedahl 1987

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

origin and evolution of a cold based tropical mountain glacier on mars the pavonis mons fan shaped deposit 1 each of the large tharsis montes volcanoes in the equatorial region of mars has an unusual amazonian aged fan shaped deposit on its west northwestern flank on the basis of viking orbiter data the origin of these deposits has been variously ascribed to volcanic mass wasting tectonic and glacial processes using new mgs and odyssey data combined with recent developments in the study of cold based glaciers we reassess the geology and mode of origin for these deposits with particular emphasis on pavonis mons the deposits share three characteristic facies including 1 a ridged facies consisting of tens to 100 parallel concentric ridges around the margins of the deposits 2 a knobby facies composed of irregular hills and hummocks and 3 a smooth facies of broad lobate plains that superposes all other units within the deposits on the basis of morphology topography superposition relationships and close terrestrial analogs in the dry valleys of antarctica we interpret the pavonis fan shaped deposit as the depositional remains of a cold based glacier that formed on the northwestern flank in recent martian history we interpret the ridged facies as drop moraines formed around the margins of a retreating cold based glacier the knobby facies as a sublimation till derived from in situ down wasting of cold based glacial ice and the smooth facies as extant debris covered glacial ice in addition to the three main facies the fan shaped deposit at pavonis mons contains several unique features including arcuate scarps high relief flow like features and radial ridges which suggest that volcanism played a role during its formation using recent results from mars general circulation model simulations we outline a model of glacier formation involving atmospheric deposition of water ice on the northwestern flanks of the tharsis montes during periods of high mean obliquity reconstructed ice sheet profiles for each of the tharsis montes glaciers suggest that the ice sheets attained average thicknesses of 1 6 2 4 km values that are consistent with a cold based glacial origin analysis of crater size frequency distributions using new data indicates that the age of the glaciation lies within the late amazonian 10 200 ma thus our results suggest that multiple phases of tropical mountain glaciation occurred on mars within the past few hundred myr and that significant amounts of near surface equatorial ice may remain within the deposit today

degradation of mid latitude craters on mars abstract recent geomorphic remote sensing and atmospheric modeling studies have shown evidence for abundant ground ice deposits in the martian mid latitudes numerous potential water ice rich flow features have been identified in craters in these regions including arcuate ridges gullies and small flow lobes previous studies such as in newton basin have shown that arcuate ridges and gullies are mainly found in small craters 2 30 km in diameter these features are located on both pole facing and equator facing crater walls and their orientations have been found to be dependent on latitude we have conducted surveys of craters 20 km in diameter in two mid latitude regions one in the northern hemisphere in arabia terra and one in the southern hemisphere east of hellas basin in these regions prominent lobes potentially ice rich are commonly found on the walls of craters with diameters between 20 100 km additional water ice rich features such as channels valleys alcoves and debris aprons have also been found in association with crater walls in the eastern hellas study region channels were found to be located primarily on pole facing walls whereas valleys and alcoves were found primarily on equator facing walls in the arabia terra study region these preferences are less distinct in both study regions lobate flows gullies and arcuate ridges were found to have pole facing orientation preferences at latitudes below 45 and equator facing orientation preferences above 45 similar to preferences previously found for gullies and arcuate ridges in smaller craters interrelations between the features suggest they all formed from the mobilization of accumulated ice rich materials the dependencies of orientations on latitude suggest a relationship to differences in total solar insolation along the crater walls differences in slope of the crater wall differences in total solar insolation with respect to wall orientation and variations in topography along the crater rim can explain the variability in morphology of the features studied the formation and evolution of these landforms may best be explained by multiple cycles of deposition of ice rich material during periods of high obliquity and subsequent modification and transport of these materials down crater walls

morphology and composition of the surface of mars mars odyssey themis results the thermal emission imaging system themis on mars odyssey has produced infrared to visible wavelength images of the martian surface that show lithologically distinct layers with variable thickness implying temporal changes in the processes or environments during or after their formation kilometer scale exposures of bedrock are observed elsewhere airfall dust completely mantles the surface over thousands of square kilometers mars has compositional variations at 100 meter scales for example an exposure of olivine rich basalt in the walls of ganges chasma thermally distinct ejecta facies occur around some craters with variations associated with crater age polar observations have identified temporal patches of water frost in the north polar cap no thermal signatures associated with endogenic heat sources have been identified

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

meltback of hesperian aged ice rich deposits near the south pole of mars evidence for drainage channels and lakes ponding minimum volumes 10 12 m 3 overtopping downcutting and further drainage of material through a series of craters and into the prometheus basin near the edge of the current cap topography data show that water filled some craters to depths of at least 200 m and possibly as much as 600 m materials derived from melting of this lobe of the daf drained over a lateral distance of 600 km and a vertical height of 800 m partially emptying into the prometheus basin these combined observations imply that meltback of the older volatile rich deposit was a widespread event occurring on both sides of the deposit over a distance of at least 1800 km and in an area possibly as much as 2 9 10 6 km 2 candidate top down and bottom up melting scenarios are examined the presence of associated hesperian aged volcanic deposits and possible subglacial edifices suggests that local and regional basal heating was a major factor in generating the meltwater that formed the drainage features index terms 6225 planetology solar system objects mars 5416 planetology solid surface planets glaciation 5470 planetology solid surface planets surface materials and properties 3309 meteorology and atmospheric dynamics climatology 1620 5418 planetology solid surface planets heat flow keywords mars polar glaciers hesperian channels water

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

improving a tree ring reconstruction from west central scandinavia 900 years of warm season temperatures dendroclimatological sampling of scots pine pinus sylvestris l has been made in the province of jamtland in the west central scandinavian mountains since the 1970s the tree ring width trw chronology spans several thousand years and has been used to reconstruct june august temperatures back to 1632 bc a maximum latewood density mxd dataset covering the period ad 1107 1827 with gap 1292 1315 was presented in the 1980s by fritz schweingruber here we combine these historical mxd data with recently collected mxd data covering ad 1292 2006 into a single reconstruction of april september temperatures for the period ad 1107 2006 regional curve standardization rcs provides more low frequency variability than non rcs and stronger correlation with local seasonal temperatures 51 variance explained the mxd chronology shows a stronger relationship with temperatures than the trw data but the two chronologies show similar multi decadal variations back to ad 1500 according to the mxd chronology the period since ad 1930 and around ad 1150 1200 were the warmest during the last 900 years due to large uncertainties in the early part of the combined mxd chronology it is not possible to conclude which period was the warmest more sampling of trees growing near the tree line is needed to further improve the mxd chronology

the dispersal of pyroclasts from ancient explosive volcanoes on mars implications for the friable layered deposits a number of voluminous fine grained friable deposits have been mapped on mars the modes of origin for these deposits are debated the feasibility for an origin by volcanic airfall for the friable deposits is tested using a global circulation model to simulate the dispersal of pyroclasts from candidate source volcanoes near each deposit it is concluded that the medusae fossae formation and electris deposits are easily formed through volcanic processes and that the hellas deposits and south polar pitted deposits could have some contribution from volcanic sources in specific atmospheric regimes the arabia and argyre deposits are not well replicated by modeled pyroclast dispersal suggesting that these deposits were most likely emplaced by other means

mesoscale pigment fields in the gulf stream observations in a meander crest and trough in september october 1988 and april 1989 a series of hydrographic transects were completed across the gulf stream front in a meander crest and meander trough respectively one of the main experimental objectives was to relate the spatial distribution of chlorophyll to the physical fields of gulf stream meanders chlorophyll distributions are derived from conductivity temperature depth ctd fluorescence profiles calibrated with discrete pigment samples collected from bottles at several depths at various stations objective analysis oa maps and vertical sections in stream coordinates of chlorophyll on density surfaces show the chlorophyll distribution was strongly related to the structure of the gulf stream front in particular chlorophyll concentrations greater than 0 4 mg m 3 were at or inshore of the gulf stream north wall characteristic length scales of chlorophyll distribution determined from the horizontal and temporal correlation function are the same order 50 100 km as length scales of the physical variables the maximum chlorophyll concentrations in the vertical were from the surface to 50 m depth on the western flank of the meander crest and deepened to 75 to 100 m depth on the eastern flank this coincides with the deepening of the 24 4 25 7 surfaces from the western to the eastern flank of the meander crest although in the spring cruise the maximum chlorophyll concentrations were also found at depths between the surface and 100 m there were no clear distinctions in pigment distributions between the western and eastern transects of a relatively weak trough maximum chlorophyll concentrations 1 0 1 5 mg m 3 from the 1989 spring bloom in slope waters were about double those observed in the 1988 fall data the primary physical mechanisms influencing the mesoscale pigment distribution in gulf stream meanders observed in this study are 1 outcropping of nutrient bearing strata in the spring 2 meander induced upwelling of nutrients along sloping isopycnals and 3 gulf stream ring interactions

global duricrust on mars analysis of remote sensing data global remote sensing data for mars are analyzed to obtain a simple self consistent model for the surface layer the data sets discussed include radar cross section measurements at several wavelengths radio whole disk thermal emission observations at two wavelengths the global distribution of thermal inertia deviations of diurnal temperatures from those of a homogeneous model and thermal spectral estimates of surface rock abundance and of the thermal inertia of the nonrocky component of the surface the data sets which most constrain the interpretation are the rock abundance map and the correlation of thermal inertia with radar cross section these require the rock abundance to not vary significantly from place to place and simultaneously require the density and thermal inertia of the fines to vary in a consistent manner the simplest model which can explain all of the data involves a global case hardened crust duricrust which varies spatially in its degree of formation in general low thermal inertia regions have a poorly developed crust and highinertia regions have a well developed crust there are however regions that consist of coarse particles and which do not fit this model e g chryse this model is consistent with the ages of low inertia regions and with aeolian mechanisms for their development the duricrust is thought to form via the mobilization of salt ions within a layer of water adsorbed within the regolith and its formation may be associated with the exchange of water between the regolith and atmosphere which occurs on the 105 and 106 year time scale

3d soft sediment deformation structures evidence for quaternary seismicity in the madrid basin spain three dimensional patterns of soft sediment deformation affecting middle pleistocene fluvial deposits in the lower manzanares valley sw madrid city are reported they promote a small scale hummocky topography defined by different sized domes mud volcanoes wavy ridges and fissures on an ancient flood plain surface related channel fill deposits are pervasively dewatered indicating liquefaction the sedimentological context reveals that the deformation of both floodplain surface and channel fill deposits were contemporaneous singular deformed level and generated at or near the ground surface this rules out the possibility of sediment loading and indicates a possible earthquake induced origin

geomorphic analysis of lobate debris aprons on mars at mars orbiter camera scale evidence for ice sublimation initiated by fractures 1 lobate debris aprons known to be geomorphic landform indicators of the presence of ground ice are of special interest for future missions devoted to the research of water on mars lobate debris aprons in fretted terrains of deuteronilus and protonilus mensae 35 50 n show typical convex shapes interpreted to be the result of viscous deformation at the scale of mars orbiter camera moc high resolution images the surface of these debris aprons shows complex patterns with small pits and buttes these patterns can be explained by the mantling of dust the accumulation of interstitial ice and the subsequent removal of ice by sublimation the sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures theoretical quantification of sublimation rates therefore minimizes sublimation which is not a homogeneous process at least over the landforms studied crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past in the point of view of future searching of subsurface ice only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform the geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations especially in order to measure current sublimation of ground ice

a sedimentary origin for intercrater plains north of the hellas basin implications for climate conditions and erosion rates on early mars understanding the origin volcanic or sedimentary and timing of intercrater plains is crucial for deciphering the geological evolution of mars we have produced a detailed geological map of the intercrater plains north of the hellas basin based on images from the mars express high resolution stereo camera the mars reconnaissance high resolution imaging science experiment and context erosional windows and fresh impact craters provide a way of studying the lithology of intercrater plain units they are composed predominantly of light toned sedimentary rocks with subhorizontal bedding over a broad extent greater than tens of kilometers showing cross bedding stratifications locally the broad extent geometry and flat topography of these sediments favor a formation by aqueous processes alluvial and lacustrine rather than airfall eolian and volcaniclastic the late noachian 3 7 ga sedimentary plains are locally covered by dark toned rough textured lava flows of late hesperian age 3 3 ga fe mg phyllosilicates were detected within sedimentary rocks whereas volcanic rocks contain pyroxene and lack signatures of alteration in agreement with interpretations made from texture and morphology in erosional windows the superimposition of sedimentary rocks by younger volcanic flows enables the estimation of an erosion rate of 1000 nm yr 1 during the hesperian period 3 3 3 7 ga thus our study shows that an intense sedimentary cycle occurred on the northern rim of the hellas basin before and during the late noachian leading to the formation of widespread sedimentary plains which were then eroded in agreement with a gradual change in the climatic conditions in this period and later covered by volcanic flows

the age and origin of the labyrinth western dry valleys antarctica evidence for extensive middle miocene subglacial floods and freshwater discharge to the southern ocean a 50 km long network of bedrock channels and scoured terrain occupies the ice free portion of a major trough that crosses the transantarctic mountains in southern victoria land the channels collectively termed the labyrinth emerge from beneath the margin of the east antarctic ice sheet wright upper glacier and are incised into a 300 m thick sill of ferrar dolerite at the head of wright valley upper and intermediate elevation erosion surfaces of the labyrinth exhibit striations and molding characteristic of glacial erosion channels and canyons on the lower surface are as much as 600 m wide and 250 m deep have longitudinal profiles with many reverse gradients and contain potholes 35 m deep at tributary junctions these characteristics are most consistent with incision from fast flowing subglacial meltwater estimated discharge is on the order of 1 6 2 2 10 6 m 3 s 1 our 40 ar 39 ar analyses of volcanic tephra from the labyrinth show that the chan nels are relict that major channel incision predates 12 4 ma and that the last major subglacial flood occurred sometime between 14 4 ma and 12 4 ma the most plausible origin for the labyrinth is erosion associated with episodic drainage of subglacial lakes in east antarctica one compelling possibility is that discharge of large volumes of sub glacial meltwater to the southern ocean and to the ross sea in particular may have coincided with and contributed to oscillations in regional and or global climate during the middle miocene

recent and episodic volcanic and glacial activity on mars revealed by the high resolution stereo camera the large area coverage at a resolution of 10 20 metres per pixel in colour and three dimensions with the high resolution stereo camera experiment on the european space agency mars express mission has made it possible to study the time stratigraphic relationships of volcanic and glacial structures in unprecedented detail and give insight into the geological evolution of mars here we show that calderas on five major volcanoes on mars have undergone repeated activation and resurfacing during the last 20 per cent of martian history with phases of activity as young as two million years suggesting that the volcanoes are potentially still active today glacial deposits at the base of the olympus mons escarpment show evidence for repeated phases of activity as recently as about four million years ago morphological evidence is found that snow and ice deposition on the olympus construct at elevations of more than 7 000 metres led to episodes of glacial activity at this height even now water ice protected by an insulating layer of dust may be present at high altitudes on olympus mons

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

photogeologic mapping and the geologic history of the hellas basin floor mars abstract the hellas basin on mars is the second largest topographically well defined impact structure in the solar system and has repeatedly been interpreted as a major sink of volcanic glacio fluvial and eolian materials based on established guidelines for planetary mapping we compiled a comprehensive photogeological map of hellas planitia i e the hellas basin floor 1 2 000 000 1 8 106 km2 see supplementary online material using the thermal emission imaging system themis ir day time mosaic as basemap supplemented by several other datasets we identified 33 units which were categorized into a rim assemblage containing dissected units a layered rim sequence and other basin rim units as well as a floor assemblage containing the honeycomb formation an interior formation and a plains sequence relative dating of units was performed wherever contacts revealed stratigraphic relationships and was complemented by absolute model ages amas of all units that lend themselves to reliable crater size frequency distribution csfds measurements on the basis of our results as well as amas of circum hellas volcanic provinces by previous authors we compiled a chronostratigraphic model of the hellas basin floor the northern basin rim shows evidence vast layered hydrous mineral bearing deposits containing meandering channel like valleys that the early history of the basin until 3 8 ga ago experienced extended periods of low energy fluvial and possibly lacustrine activity superposing the layered rim sequence the majority of the hellas basin infill 1 5 1 7 106 km3 consists of volcanic material a lower and an upper wrinkle ridged plains unit which was shortened by a compressive stress field relatively soon after its emplacement based on their ages and stratigraphic considerations we identified malea patera and possibly also tyrrhena patera as a suitable source for the older lower plains 3 8 ga and hadriaca and or amphitrites paterae for the younger upper plains 3 7 ga shortly after these volcanic episodes the entire basin floor was covered by large amounts of deposits 106 km3 containing aqueously altered mafic materials we interpret the deposits to have originated from hesperia planum and the hesperia hellas trough where they might have been removed by glacio fluvial processes which also sculpted the hellas rim sections along northern promethei terra and malea planum around the same time such an apparent correlation between nearby volcanic activity and increased erosion deposition is in agreement with previous models which suggest outgassing by a maximum in global volcanism at that time caused warmer episodes enabling repeated subaerial water run off after the emplacement of these deposits intense erosion likely deflation along a rim parallel annulus began to exhume the outer parts of the wrinkle ridged plains again forming an interior formation of more elevated erosional remnants including the alpheus colles since 3 7 ga ago fluvial activity of dao niger and harmakhis valles dissected the eastern plains and emplaced pancake shaped deposits in the basin center later deflation and abrasion by katabatic winds moving through the hellas basin in a clock wise direction parallel to the basin floor outline carved out the northwestern hellas planitia trough called peneus palus possibly within a time span of few hundreds of ma or less within the amazonian being consistent with erosional patterns we observed within the basin circulation models predict such winds to be ongoing today and might thus have recently exhumed the so called honeycomb formation on parts of peneus palus this enigmatic unique terrain was possibly formed by ductile deformation of pre 3 8 ga material and appears to be partially covered by another unique landform the banded terrain although we cannot rule out that it is the surface expression of a thicker unit the banded terrain might represent flows of volatile rich airfall deposits emplaced along the edges of the hellas wind alley by turbulent marginal wind currents which currently recently prevail on both sides of the hellas planitia trough in summary our investigations enabled us to draw an updated comprehensive and self consistent picture of the geologic evolution of the hellas basin floor including volcanic peri glacial fluvial and eolian processes their possible interactions and the implications on the climatic and geologic development of the circum hellas region and the entire planet

sub kilometre intra crater mounds in utopia planitia mars character occurrence and possible formation hypotheses abstract at the middle latitudes of utopia planitia 35 45 n 65 101 e hundreds of small sized mounds located in sub kilometre impact craters dot the landscape their shape varies from circular to crescentic and their height ranges from 10 to 50 m often metre to decametre pitting is observed as is metres thick banding or stratification mound albedo is relatively high i e 0 16 the plain s terrain in the region previously linked to the latitude dependent mantle ldm of ice dust displays pitting and albedo similar to the small intra crater mounds some workers have suggested that the mounds and the plain s terrain share a common ice dust origin if so then scrutinising the mounds could provide analogical insight on the key geological characteristics and spatial distribution of the ldm itself other workers have hypothesised that the mounds are eroded sedimentary landforms or periglacial mounds underlain by a perennial ice core closed system pingos in this article we develop and then discuss each of the three mound hypotheses in a much more substantial manner than has been done hitherto towards this end we use high resolution images present a detailed regional map of mound distribution and establish a regional platform of topographical analysis using mola data superposed on a large scale ctx mosaic although the ice dust hypothesis is consistent with some observations and measurements we find that a loess based sedimentary hypothesis shows greater plausibility of the three hypotheses evaluated the pingo or periglacial one is the weakest

the hypanis valles delta the last highstand of a sea on early mars one of the most contentious hypotheses in the geological history of mars is whether the northern lowlands ever contained an oceanic water body arguably the best evidence for an ocean comes from the presence of sedimentary fans around mars dichotomy boundary which separates the northern lowlands from the southern highlands here we describe the palaeogeomorphology of the hypanis valles sediment fan the largest sediment fan complex reported on mars area 970 km2 this has an extensive catchment 4 6 x 105 km2 incorporating hypanis and nanedi valles that we show was active during the late noachian early hesperian period 3 7 ga the fan comprises a series of lobe shaped sediment bodies connected by multiple bifurcating flat topped ridges we interpret the latter as former fluvial channel belts now preserved in inverted relief meter scale thick sub horizontal layers that are continuous over tens of kilometres are visible in scarps and the inverted channel margins the inverted channel branches and lobes are observed to occur up to at least 140 km from the outlet of hypanis valles and descend 500 m in elevation the progressive basinward advance of the channellobe transition records deposition and avulsion at the margin of a retreating standing body of water assuming the elevation of the northern plains basin floor is stable we interpret the hypanis sediment fan to represent an ancient delta as opposed to a fluvial fan system at its location at the dichotomy boundary the hypanis valles fan system is topographically open to chryse planitia an extensive plain that opens in turn into the larger northern lowlands basin we conclude that the observed progradation of fan bodies was due to basinward shoreline retreat of an ancient body of water which extended across at least chryse planitia given the open topography it is plausible that the hypanis fan system records the existence last highstand and retreat of a large sea in chryse planitia and perhaps even an ocean that filled the northern plains of mars

fluvial and lacustrine activity on layered deposits in melas chasma valles marineris mars 1 valley networks on mars are the most obvious features attesting that different geologic processes and possibly climatic conditions existed in the past themis images reveal valley networks within melas chasma in valles marineris a hesperian age canyon system the valley networks in melas chasma are dense and highly organized and the heads of the valleys are scattered at different elevations all these features suggest that the networks were fed by precipitation the morphological details reveal inner channels on some valley floors attesting that water flowed within these valleys on the dem the valleys flow into a completely enclosed depression the edge of this feature follows a mola contour line and the depression shows many sedimentary morphologies suggesting lacustrine environment these landforms are located on remnants of layered deposits possibly composed of sulfate layers suggesting that fluvial activity could have contributed to the erosion of the layered terrains in valles marineris collectively the features in melas chasma are a maximum of hesperian in age these results suggest that warm wet environmental conditions on mars persisted through the hesperian and were present during the formation of valles marineris the evidence for a paleolake in melas chasma attests to adequate environmental conditions for life development through the hesperian period

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

evidence for paleolakes in erythraea fossa mars implications for an ancient hydrological cycle there is now widespread agreement that the surface of mars underwent some degree of fluvial modification but there is not yet full understanding of its surface hydrological cycle and the nature of standing bodies of water rivers and precipitation that affected its surface in this paper we explore erythraea fossa 31 5 w 27 3 s a graben adjacent to holden crater which exhibits strong evidence that it once housed a chain of three lakes had overland water flow and was subject to precipitation the inlet valley outlet valley and fan morphologies in the paleolakes are used to qualitatively discern the hydrologic history of the paleolakes based on topography constraints the three basins combined once held 56 km 3 of water depositional features within the basins that change with drainage area and nearby valleys that start near drainage divides indicate that the paleolakes may have been fed by precipitation driven runoff this suggests the presence of an atmosphere at least locally that was capable of supporting a hydrological cycle

coupling between a glacier and a soft bed ii model results the relation between the local effective pressure and shear stress on till beneath storglaciaren sweden discussed in iverson and others 1999 provides an empirical basis for studying the processes that control the strength of the ice bed coupling particles in the bed that protrude into the glacier sole support shear stresses that are limited by either ploughing or the traditional sliding mechanisms model calculations based on studies of cone penetration through fine grained sediment and sliding theory agree with the observed relation between shear stress and effective pressure if the water layer at the ice bed interface is assumed to thicken rapidly as the effective pressure approaches zero studies of the hydraulics of linked cavities provide support for this assumption if the mean thickness of the water layer reflects the extent of microcavity development at the interface comparison of the calculated shear stress with the ultimate strength of till suggests that bed deformation limits the shear stress on till beneath storglaciaren only at intermediate effective pressures at very low effective pressures like those inferred at the site of the tiltmeter discussed in iverson and others 1999 and at sufficiently high effective pressures ploughing and sliding should focus motion near the glacier sole a calculation using parameter values appropriate for ice stream b west antarctica suggests that ploughing may occur there at shear stresses not sufficient to deform the bed at depth this conclusion is reinforced by the likelihood that pore pressures in excess of hydrostatic should develop down glacier from ploughing particles thereby weakening the bed near the glacier sole however given the apparent sensitivity of the ice bed coupling to basal conditions that may be highly variable any blanket assumption regarding the flow mechanism of ice masses on soft beds should probably be viewed with skepticism

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

martian layered fluvial deposits implications for noachian climate scenarios 1 fluvial deposits in a basin north of holden crater exhibiting a sinuous anabranching pattern are of deltaic or fan origin channel width and meander wavelength indicate persistent flow magnitudes of about 700 m3 s if these flows were produced by quasi periodic climate episodes involving typical terrestrial style precipitation the deposit required thousands to millions of years to accumulate however a scenario of deposition during a few short episodes of constant heavy precipitation resulting from large impacts cannot be excluded

soft sediment deformation by kelvin helmholtz instability a case from dead sea earthquakes abstract the standard explanation for soft sediment deformation is associated with overturn of inverted density gradients however in many cases observations do not support this interpretation here we suggest an alternative in which stably stratified layers undergo a shear instability during relative sliding via the kelvin helmholtz instability khi mechanism triggered by earthquake shaking dead sea sediments have long stood out as a classical and photogenic example for recumbent folding of soft sediment these billow like folds are strikingly similar to khi structures and have been convincingly tied to earthquakes our analysis suggests a threshold for ground acceleration increasing with the thickness of the folded layers the maximum thickness of folded layers order of decimeters corresponds to ground accelerations of up to 1 g such an acceleration occurs during large earthquakes recurring in the dead sea

evidence for extensive denudation of the martian highlands high resolution topographic data from the mars orbiter laser altimeter reveal evidence for widespread denudation from margaritifer sinus to northern arabia terra an area of 1 107 km2 a major resurfacing event is indicated by 1 a heavily degraded landscape hosting numerous inliers 2 truncation or absence of valley networks and 3 a break in slope at the edge of early to middle noachian plateau materials geomorphic mapping was completed on the type locale of denudation 0 30 s 0 30 w superposition relations and crater counts for geomorphic units indicate that large scale resurfacing took place in the late noachian eroding the martian highlands and resulting in transportation and deposition of 4 5 106 km3 of sediment in the northern plains this is equivalent to a 120 m thick uniform layer of sediment on the surface of mars north of 30 n geomorphic mapping and crater counts limit the timing of denudation to the late noachian an interval of 350 500 m y using this limit we estimate a minimum rate of denudation of 2 0 m yr comparable to denudation of typical slopes in a temperate maritime climate on earth the morphology rate of denudation and extensive nature of upland degradation suggest that precipitation fed surface runoff is the most likely geomorphic agent capable of such a process indicative of a warm wet mars during the late noachian epoch

mantled and exhumed terrains in terra meridiani mars 1 hematite bearing deposits in the terra meridiani region of mars constitute the top stratum of a partially eroded layered complex that covers dissected noachian aged cratered terrain the hematite unit consists of dark plains and dunes covering a bright substrate this substrate is fully exposed beyond the borders of the hematite bearing deposit and consists of polygonal ground separated by ridges or valleys together with layered deposits that have been eroded into a variety of landforms the complex is partially covered by a regional scale aeolian mantle that thickens toward the north the hematite bearing stratum exhibits low albedoes pulse widths and intermediate thermal inertias whereas the underlying unit exhibits high values of these parameters both units have spectral emissivity signatures similar to those for the low albedo cratered terrain to the south with the addition of hematite for the top stratum the complex is interpreted to consist of extensive plains forming lava flows and tephra deposits emplaced during an extensional regime and at least partially buried by an aeolian mantle aeolian stripping of the mantle exposed much of the complex and differentially eroded the deposits to produce the landforms existent today exploration of the hematite bearing deposits by the 2003 mars exploration rover opportunity will allow testing of the hypotheses presented since this stratum has been locally reworked into dunes that only partially cover the underlying brighter portion of the complex in particular the rover based measurements will allow us to test the extent to which the unusual remote sensing properties of the units indicate aqueous alteration

complex geology of two large impact craters in tyrrhena terra mars detailed analysis using mex hrsc camera data 1 tyrrhena terra located just north of the roughly 200 km hellas impact basin is a typical region of the ancient cratered southern highlands on mars its base material is a mixture of hellas ejecta prebasin remnants and highland terrain all later saturated with smaller 200 km impact craters fluvial and lacustrine deposits erosion tectonic movements volcanic materials and aeolian processes have subsequently modified the region further in this study we take a closer look at two adjacent unnamed craters in tyrrhena terra located at 24 5 s 80 8 e crater a and 23 9 s 79 3 e crater b the craters are covered by the 20 80 m pixel mars express high resolution stereo color imager hrsc multispectral data which together with moc themis and mola data sets allows us to make very detailed analysis of the area we describe several identified geological and geomorphological units with their individual characteristics e g morphology color cratering records and elevation differences and interpret their individual evolution the crater floors show several unique material types of both depositional and erosional origin crater a has a large 200 m high central massif and a central peak ring as well as a unique low lying terrain type honeycomb terrain with narrow 50 200 m high ridges and intervening pits additionally both craters exhibit erosional features similar to each other and nearby craters indicating episodes of deposition of various material types in both craters we find that the crater pair reveals many characteristics which are typical of the n hellas rim but are not found elsewhere

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

morphology and geology of the ild in capri eos chasma mars from visible and infrared data abstract layered deposits have been observed in different locations at the surface of mars as crater floors and canyons systems their high interest relies in the fact they imply dynamical conditions in their deposition medium indeed in opposition to most of the rocks of the martian surface which have a volcanic origin bright layered deposits seems to be sedimentary outcrops capri chasma a canyon located at the outlet of valles marineris exhibits such deposits called interior layered deposits ild a large array of visible and infrared spacecraft data were used to build a geographic information system gis we added hirise images from the recent mro mission which offer a spatial resolution of 25 cm per pixel it allowed the mapping and the analysis of morphologies in the canyon we highlighted that the ild are several kilometers thick and flat top stratified deposits they overlap the chaotic floor they are surrounded and cut by several flow features that imply that liquid water was still acting after the formation of these stratified deposits the density of crater on the floor of capri chasma was quantified the current topography was aged to 3 gyr all these morphological information allow us to suggest a plausible geological history for capri chasma we propose that the interior layered deposits have formed during the hesperian during or after the opening of the canyon some observations argue that water discharges have happened at several times before and just after the formation of the ild liquid water must have played a major role in the formation of these deposits after 3 5 gyr implying that it was present in surface at least locally and temporarily if this can be applied to ild in others canyons of valles marineris it would imply that liquid water was stable in surface or sub surface during the hesperian or in the actual conditions with a cold and dry martian surface long term standing water bodies are not possible thus we suggest that either the climate at the hesperian was cold but wetter or as warm as the noachian climate what is less likely nevertheless the global climate change which has occurred at the beginning of mars history may have been later than announced

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

an analysis of open basin lake deposits on mars evidence for the nature of associated lacustrine deposits and post lacustrine modification processes abstract a large number of candidate open basin lakes low lying regions with both inlet valleys and an outlet valley have been identified and mapped on mars and are fed by valley network systems that were active near the noachian hesperian boundary the nature of processes that modified the open basin lake interiors subsequent to lacustrine activity and how frequently sedimentary deposits related to lacustrine activity remain exposed has not been extensively examined an analysis of 226 open basin lakes was undertaken to identify evidence for 1 exposed deposits of possible lacustrine origin and 2 post lacustrine activity processes that may have modified or resurfaced open basin lakes spectroscopic data from the compact reconnaissance imaging spectrometer for mars crism instrument were analyzed over identified exposed open basin lake deposits to assess the mineralogy of these deposits particular attention was paid to the possible detection of any component of aqueous alteration minerals e g phyllosilicates hydrated silica zeolites or evaporites e g carbonates sulfates chlorides associated with these exposed deposits the aim of this paper is to act as a broad survey and cataloguing of the types of lacustrine and post lacustrine deposits that are present within these 226 paleolake basins results of the morphologic classification indicate that 79 open basin lakes 35 of the population contain exposed deposits of possible lacustrine origin identified on the basis of fan delta deposits layered deposits and or exposed floor material of apparent lacustrine origin additionally all 226 open basin lakes examined appear to have been at least partially resurfaced subsequent to their formation by several processes including volcanism glacial and periglacial activity impact cratering and aeolian activity results from the analysis of crism data show that only 10 29 of the 34 deposits with crism coverage of the exposed open basin lake deposits contain positively identified aqueous alteration minerals with one deposit also containing evaporites the identified hydrated and evaporite minerals include fe mg smectite kaolinite hydrated silica and carbonate with fe mg smectite the most commonly identified mineral these results indicate that hydrated and evaporite minerals are not as commonly associated with lacustrine deposits on mars as they are on earth this suggests in situ alteration and mineral precipitation a common source of such minerals in terrestrial lakes was not a major process occurring in these paleo lacustrine systems and that the observed minerals are likely to be present as transported material within the lacustrine deposits the lack of widespread in situ alteration also suggests that either the water chemistry in these paleolake systems was not conducive to aqueous alteration and mineral precipitation or that the open basin lake systems were relatively short lived

styles and timing of volatile driven activity in the eastern hellas region of mars 1 recent analyses of mars global surveyor and mars odyssey data sets provide new insights into the geologic evolution of the eastern hellas region of mars in particular the role of volatiles here we present results of our recent work and integrate these with previous studies by various investigators to provide a synthesis of the history of volatile driven activity of the region we utilize high resolution images from the mars orbiter camera and thermal emission imaging system combined with mars orbiter laser altimeter digital elevation models and profiles to examine fluvial systems that dissect the circum hellas highlands to characterize stages in the development of the dao niger harmakhis and reull valles canyon systems and to evaluate evidence for ancient lakes in hellas planitia the occurrence of valley networks dissected highland crater rims and crater interior deposits such as layered plateaus suggests widespread ancient degradation of the circum hellas highlands canyon development which represents subsequent more localized activity may have included an early fluvial phase followed by the collapse and sapping dominated stages that along with recent wall erosion and floor resurfacing produced the currently observed morphologies the prominent role of collapse and sapping along the east rim of hellas along with the presence of numerous channels extending toward the basin and sequences of finely layered deposits along the basin rim suggests a volatile rich substrate across a broad depositional shelf the east rim of the basin was an accumulation zone for atmospheric volatiles and or the edge of volatile rich deposits associated with the basin floor this evidence combined with topographic data and cratered terrain preservation around the basin is consistent with a lacustrine period or periods in early martian history the style magnitude and spatial extent of volatile driven activity in eastern hellas have varied considerably with time and these variations may represent a transition from a water to an ice dominated surface environment

ancient ocean on mars supported by global distribution of deltas and valleys the climate of early mars could have supported a complex hydrological system analysis of ancient deltaic deposits and valley networks reveals the presence of a planet wide equipotential surface in the northern lowlands indicative of the existence of a vast ocean on mars 3 5 billion years ago

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

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

thermal and near infrared analyses of central peaks of martian impact craters evidence for a heterogeneous martian crust central peaks of impact craters contain materials exhumed from depth and therefore investigation of these materials provides clues to subsurface geology and mineralogy a global spectral survey of central peaks of martian impact craters between 10 and 200 km diameter was completed using mars odyssey thermal emission imaging system themis data twenty six central peaks with distinctive spectral signatures from surrounding plains were identified and characterized with thermal infrared and visible near infrared data the distribution of spectrally distinct central peaks sdcps shows some degree of regional clustering with most craters found in western noachis terra tyrrhena terra within the northern rim of hellas basin and fewer in the northern lowlands with the exception of four craters in western noachis terra sdcps contain only one spectrally distinct unit at themis resolution 100 m pixel the maximum number of spectrally distinct units observed was three in jones and ostrov craters the western noachis terra sdcps may expose crustal stratigraphies of multiple igneous compositions or impact materials from argyre in the highlands most sdcp units are consistent with enrichments in olivine or pyroxene relative to surrounding plains suggesting olivine and pyroxene basaltic lithologies few are olivine and pyroxene poor no spatial trend in spectrally derived compositions of sdcps was observed three sdcps contain themis signatures consistent with high abundances of phyllosilicates which may contain the most phyllosilicate rich lithologies found in central peak associated materials globally

geophysical evidence of multiple glacier advances in lago fagnano 54 s southernmost patagonia the island of tierra del fuego at the southernmost extreme of patagonia is located in one of the most extensively glaciated areas of the southern hemisphere outside antarctica during the late pleistocene the lago fagnano region at w54 30 0 s and w68 w has experienced several phases of glacier growth and retreat since the last glacial maximum lgm we illustrate these phases using combined geomorphological geophysical and coring surveys in lago fagnano itself a w105 km long e w oriented glaciotectonic basin we identify and map a complex set of submerged frontal central and lateral moraines covered by lacustrine sediments using seismic stratigraphic analysis of multi channel profiles imaging the sub lake floor we then combine these geophysical data with field observations and regional maps of similar structures around the lake to reconstruct the spatial behavior of the fagnano paleo glacier since the lgm we interpret the preserved frontal moraines as having formed during at least 20 re advance stages of the glacier within a long term deglaciation interval post lgm preliminary tephrochronological dating of a w7 5 m long core indicates a step wise deglaciation pattern comprising a final glacier re advance stage at w11 2 ka bp

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

sedimentary history and mass flow structures of chryse and acidalia planitiae mars geologic mapping and crater counting in chryse and acidalia planitiae cap reveal five major sedimentary deposits of hesperian to early amazonian age including 1 a mass flow deposited during the early hesperian near deuteronilus mensae northeast of the map region that may have resulted from the carving of kasei valles 3000 km southwest of the exposed part of the deposit 2 knobby plains material consisting of channel likely from simud and tiu valles and possibly ares and shalbatana valles and mass wasting deposits in central and eastern cap 3 material largely from maja and ares valles emplaced in at least western and southern cap outcrops in southern chryse planitia developed thermokarst 4 a thin mass flow covering much of southern chryse planitia that emanated from simud and tiu valles and 5 a thick extensive perhaps 3500 km across mass flow deposit in central and northern cap derived from accumulation and backflow of the preceding thin mass flow or perhaps melting of polar deposits other possible deposits may not be recognizable owing to burial by younger materials or a lack of morphologic signature various associated landforms appear to be consistent with the mass flow interpretations including lobate and linear scarps along deposit edges fractures related to desiccation of thick sediments troughs and ridges near the edges of the deposit indicative of secondary mass movement and deformation pitted domes and fissure fed flows possibly formed by sedimentary mud eruptions and longitudinal channel grooves perhaps formed by roller vortices no convincing evidence for paleoshorelines or stagnant ice sheets is found in cap these findings suggest that mass flow and hyperconcentrated flooding may have been the predominant processes of outflow channel dissection in cap elsewhere in the northern plains similar landforms are prevalent the mass flow interpretation does not require either multiple episodes of extraordinarily high water discharge rates achieved by freeing huge volumes of water from the crust repetitive recycling of immense volumes of water into highland aquifers at the heads of chryse channels or profound climate change mars pathfinder will most likely land on and inspect the surface of the thin mass flow that originated from the canyons of simud and tiu valles

soft sediment deformation fabric in the precambrian bhander oolite central india abstract chertified oolite in the lower part of the precambrian bhander limestones around maihar madhya pradesh india shows extensive compaction deformation of ooids into oblate bodies lying preferably parallel to bedding chertification though begun locally when compaction was only slight continued through and outlasted compaction deformation in most parts unusual deformation of ooids is caused by overpressurization of ooids against a preburial rigid emersion surface below the chertified oolite unlike common fabrics of tectonically deformed rocks compaction deformation fabrics are uneven with respect to both shape and orientation of ooids though there is a strong tendency for preferred orientation of the deformed ooids parallel to bedding directional variability is not uncommon t is difference of soft sediment deformation fabric from that of tectonically deformed rocks mainly stems from the fact that overburden stress is transmitted heterogeneously from grain to grain in unconsolidated sediments lithification on the other hand homogenizes stress distribution leading to greater uniformity of shape and orientation of fabric elements in tectonically deformed rocks in addition the soft sediment deformation fabric lacks relationship with the external geometry of the rocks

regional drainage of meltwater beneath a hesperian aged south circumpolar ice sheet on mars 1 five sinuous valleys that begin near the margins of the hesperian aged dorsa argentea formation daf are examined using mars global surveyor mars orbiter laser altimeter data these valleys are carved into the surrounding noachian cratered terrain and extend away from the daf for lengths up to 1600 km before terminating in the argyre basin 1 3 km below their starting elevations the association of these valleys with the daf thought to be the volatile rich deposits of a previously widespread circumpolar ice sheet supports the scenario whereby the valleys formed contemporaneously with the daf and served as conduits for drainage of meltwater associated with the melting and retreat of the ice sheet examination of the head regions of three of the valleys reveals pits and basins carved into the local deposits of the daf closely associated with the valley heads on the basis of the distribution of these pits and basins their morphologies size spacing and basal elevations similar to the nearby valleys we conclude that the pits and basins represent the expression of the valleys within the daf we suggest that the pits and basins resulted from surface collapse of the deposits due to basal drainage of meltwater beneath the thinning ice sheet sinuous ridges within some of the basins appear similar to terrestrial eskers and further support this scenario

cold based mountain glaciers on mars western arsia mons surface environmental conditions on mars are currently extremely cold and hyperarid most equivalent to polar deserts on earth coupling newly acquired mars data with fieldbased observations regarding the flow surface morphology and depositional history of polar glaciers in antarctica we show that the multiple facies of an extensive fan shaped deposit on the western flanks of arsia mons volcano are consistent with deposition from cold based mountain glaciers an outer ridged facies that consists of multiple laterally extensive arcuate and parallel ridges resting without disturbance on both well preserved lava flows and an impact crater is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold based glacier a knobby facies that consists of equidimensional knobs each to several kilometers in diameter is inward of the ridges this facies is interpreted as a sublimation till derived from in situ downwasting of ashrich glacier ice a third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock glacier deposits some of which may still be underlain by a core of glacier ice taken together these surficial deposits show that the western flank of arsia mons was occupied by an extensive mountain glacial system accumulating on and emerging from the upper slopes of the volcano and spreading downslope to form a piedmont like fan

millochau crater mars infilling and erosion of an ancient highland impact crater the geology and stratigraphy of millochau crater 21 4 s 275 w located in the highlands of tyrrhena terra mars are documented through geomorphic analyses and geologic mapping crater size frequency distributions and superposition relationships are used to constrain relative ages of geologic units and determine the timing and duration of the geologic processes that modified millochau rim materials and emplaced deposits on millochau s floor crater size frequency distributions show a middle noachian age for rim materials and middle noachian to early hesperian ages for most of the interior deposits valley networks and gullies incised within millochau s rim materials and interior wall respectively indicate fluvial activity was an important erosional process millochau contains an interior plateau offset northeast of millochau s center which rises up to 400 m above the surrounding crater floor and slopes downward to the south and west layers exposed along the northern and eastern scarp boundaries of the plateau are tens to hundreds of meters thick and laterally continuous in moc images these layers suggest most materials within millochau were emplaced by sedimentary processes e g fluvial or eolian with the potential for lacustrine deposition in shallow transient bodies of water and contributions of volcanic airfall mass wasting may have also contributed significant quantities of material to millochau s interior especially to the deposits surrounding the plateau superposition relationships combined with impact crater statistics indicate that most deposition and erosion of millochau s interior deposits is ancient which implies that fluvial activity in this part of tyrrhena terra is much older than in the eastern hellas region eolian processes mobilized sediment to form complicated patterns of long and short wavelength dunes whose emplacement is controlled by local topography these deposits are some of the youngest within millochau amazonian and eolian modification may be ongoing

geomorphic and stratigraphic analysis of crater terby and layered deposits north of hellas basin mars received 20 september 2006 revised 12 february 2007 accepted 17 may 2007 published 24 august 2007 1 the geologic history of crater terby is developed through geomorphic and stratigraphic analyses within the regional context of the hellas basin terby exhibits 2 km thick sequences of layers that consist of repetitive subhorizontal and laterally continuous beds the layers are predominantly fine grained as indicated by their ease of aeolian erosion although a few consolidated layers weather to form rubbly talus the grain size or composition of the deposited materials fluctuated producing layering but the overall properties of the deposits are similar throughout the sequence and are comparable to layered deposits in other crater basins around hellas the original depositional geometry physical and geological characteristics of the layers in terby and the other basins lead us to favor a lacustrine origin but a loess like origin cannot be ruled out the formation of the layers corresponds to a period when the circum hellas region may have been occupied by a lake s up to 3 6 km deep once the lake in hellas decreased the layers in terby were incised by troughs and a moat like depression we attribute this erosion to scour beneath an ice cover due to a lack of integrated fluvial drainage or large aeolian deflation features the presence of viscous flow features in a crater on terby s northwestern rim and lobate features on terby s crater floor are also indicative of ice the lack of depositional features associated with the postulated glacial activity suggests there was a contemporaneous shallow ice covered lake covering the floor of terby that transported material into the greater hellas basin

topographically induced upwelling off eastern australia abstract a high resolution numerical study of an idealized western boundary current flow over variable topography is presented with application to the east australian current eac the results indicate that alongshelf topographic variations off australia s east coast cause the eac to accelerate over the narrowing continental shelf near cape byron this acceleration is sufficient to hinder the geostrophic adjustment in the bottom boundary layer bbl which would usually cause the eac driven bbl to shut down consequently a region of persistent high bottom stress was established off cape byron which was responsible for driving an upwelling bbl it is shown that the enhanced vertical mixing associated with a low richardson number flow beneath the eac reduced the local stratification consequently the burger number is decreased resulting in a long shutdown timescale of the bbl which enables a nearshore thermal to be established and maintained such fronts are commonly observed in the region as a p

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

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

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