limnologic analysis of gusev crater paleolake mars abstract the survey of the hydrogeologic system formed by gusev crater and ma adim vallis aeolis subquadrangle of mars points out evidence for the existence of an ice covered lake in gusev crater a first lake was formed by the drainage of the aquifer in the region surrounding gusev before the entry of ma adim vallis in the crater the existence of a former lake in gusev is deduced from the morphology of the ma adim delta its comparison with terrestrial antarctic analogs argues for the presence of an ice covered lake in gusev at the time that the southern part of the crater s rampart was breached by ma adim first release and for a subice lacustrine construction of the valley s delta our survey shows that ma adim vallis may have entered gusev crater as late as late hesperian early amazonian as part of a second lake episode the relationship between the variation of the gusev lake water level the volume of the lake and the surface of the lake bed is established by our bathymetric model the elevation of the former lake is deduced from the elevation of the mesa like structures in the delta of ma adim vallis furthermore the correlation of the crater frequency of gusev rampart with mars stratigraphic age shows that lakes may have occupied gusev crater over a period of time covering 2 gyrs from the formation of the crater to the last episode of water release from ma adim vallis though it is most likely that the lake was episodical the recurrence of abundant water in gusev crater makes this site a high priority for missions either for martian resource exploration or for the search of life

venusian channels and valleys distribution and volcanological implications abstract nearly complete image coverage of venus by magellan enabled us to map various venusian channel and valley landforms and to examine their associations with other geological units global mapping reveals a nonrandom distribution the highest total concentration is in the equatorial regions characterized by highlands rift and fracture zones and associated volcanic features many channels associated with flow deposits are similar to typical terrestrial lava drainage channels they are observed to be associated with a wide range of volcanic edifices such as coronae shield volcanoes and rift and fracture zones one type of channel similar morphologically to lunar sinuous rilles is classified as a venusian sinuous rille based on the close associations of many venusian sinuous rilles with coronae we hypothesize that mantle plume or blob volcanism has caused high effusion and sustained lava eruptions essential for sinuous rille formation mantle derived high temperature low viscosity lava eruptions are responsible for the efficient erosional processes particularly for thermal erosion that seems to be at least partially required for some sinuous rille formation many valley networks are observed in highlands and in association with coronae fracture systems and source zones for low viscosity lavas both key to network formation were probably concentrated at highlands and coronae canali type channels which are morphologically unlike other known volcanic channels are limited to certain plains regions a wide range of low viscosity lava types is possible for the channel forming lava depending on the formation mechanism their lengths exceed the lengths of other common volcanic channel types on venus implying a large volume of lava and long duration of the eruption the close association of canali with plains regions implies that canali formation is probably related to the emplacement of plains a hypothesized global resurfacing event late in venusian history may be responsible for canali formation

wrinkle ridge assemblages on the terrestrial planets the wrinkle ridge assemblage is a group of associated features that have been observed on the moon mars and mercury members of the wrinkle ridge assemblage are classified as either arches or ridges based on morphology and ridges are subdivided into first second or third order ridges on the basis of dimensions the ridge assemblages described in this study are known to occur in mare basalts on the moon and smooth plains units that may be volcanic in origin on mars and mercury the structures that occur in the continental flood basalts of the columbia plateau in the northwestern united states are morphologically and dimensionally similar to features in the ridge assemblages on the terrestrial planets the anticlinal ridges of the columbia plateau and many first order ridges on the moon mars and mercury are interpreted to be folds with reverse or thrust faulting developed as a result of buckling flexure fracture or buckling as a consequence of reverse or thrust faulting fracture flexure estimates of the unit shortening across first order ridges using simple geometric forms to approximate the ridge morphology are lower than those determined for the anticlines of the columbia plateau where displacements are the results of folding and reverse to thrust faulting evidence of layer parallel extension that often accompanies folds developed by fracture flexure mechanisms i e drape or fault bend folds is not found in the anticlinal ridges of the columbia plateau and has only been observed in one ridge on the moon a kinematic model involving buckling followed by reverse to thrust faulting flexure fracture is favored for the origin of the anticlinal ridges of the columbia plateau and many of the first order ridges on the moon mars and mercury

volcanology of arnus vallis mars abstract arnus vallis av is a 300 km long sinuous rille located on the northeastern flank of the syrtis major volcano on mars observational evidence presented here suggests that av formed as an open lava channel that was at least partly incised into the pre existing terrain the lava source area consists of a sub circular pit at the southwestern end of a 7 km long straight section of channel av trends down slope from this source with an average bottom slope of 0 26 or 0 14 width varies from 1 km at the source to 0 6 km near the distal end with a mean of 0 76 km depth decreases from 180 m at the source to 25 m near the distal end the av terminus is obscured by a large impact crater we suggest that the material that flowed in av must have been a relatively high temperature low viscosity lava dynamically and perhaps compositionally similar to terrestrial komatiite or some lunar basalt lavas if correct this finding has implications for the mode of construction of syrtis major

was the mangala valles system incised by volcanic flows 1 the mangala valles system of channels heads at one of the graben that comprise memnonia fossae extends northward nearly 1000 km across noachian and hesperian highlands and terminates at basins contiguous with amazonis planitia the mangala valles system has previously been interpreted to have formed through one or more catastrophic aqueous floods on the basis of similarities between the characteristics of its channel landforms and those of terrestrial systems including the channeled scabland of washington although aqueous mechanisms for formation of mangala valles are broadly congruous with known characteristics of the channel system an alternative volcanic hypothesis for formation of the system appears to be worthy of consideration on the basis of 1 its consistency with the volcanotectonic nature of the system and 2 commonalities between the basic nature of the system and that of large volcanic channels of the inner solar system estimates based on thermal considerations suggest that formation of mangala valles could conceivably have taken place through eruption of a lava volume of 2 105 km3 or roughly the total volume of the terrestrial columbia river basalt group the volcanic hypothesis for formation of mangala valles and a hybrid hypothesis involving formation of mangala valles through aqueous processes followed by or in concert with substantial modification of the system by volcanic erosion and deposition appears viable and worthy of future consideration

surficial deposits at gusev crater along spirit rover traverses the mars exploration rover spirit has traversed a fairly flat rock strewn terrain whose surface is shaped primarily by impact events although some of the landscape has been altered by eolian processes impacts ejected basaltic rocks that probably were part of locally formed lava flows from at least 10 meters depth some rocks have been textured and or partially buried by windblown sediments less than 2 millimeters in diameter that concentrate within shallow partially filled circular impact depressions referred to as hollows the terrain traversed during the 90 sol martian solar day nominal mission shows no evidence for an ancient lake in gusev crater

paleolakes and impact basins in southern arabia terra including meridiani planum implications for the formation of hematite deposits on mars 1 the hematite deposit in meridiani planum was selected for a mars exploration rover mer landing site because water could be involved in the formation of hematite and water is a key ingredient in the search for life our discovery of a chain of paleolake basins and channels along the southern margin of the hematite deposits in meridiani planum with the presence of the strongest hematite signature adjacent to a paleolake basin supports the possible role of water in the formation of the hematite and the deposition of other layered materials in the region the hematite may have formed by direct precipitation from lake water as coatings precipitated from groundwater or by oxidation of preexisting iron oxide minerals the paleolake basins were fed by an extensive channel system originating from an area larger than texas and located south of the schiaparelli impact basin on the basis of stratigraphic relationships the formation of channels in the region occurred over much of mars history from before the layered materials in meridiani planum were deposited until recently the location of the paleolake basins and channels is connected with the impact cratering history of the region the earliest structure identified in this study is an ancient circular multiringed basin 800 1600 km diameter that underlies the entire meridiani planum region the mer landing site is located on the buried northern rim of a later 150 km diameter crater this crater is partially filled with layered deposits that contained a paleolake in its southern portion

fluid lava flows in gusev crater mars 1 rocks on the floor of gusev crater are basaltic in composition as determined from measurements by the mars exploration rover spirit on the basis of compositional data models of the basaltic lavas at the time of their emplacement suggest viscosities of 2 3 to 50 pa s dependent on the number of phenocrysts and vesicles that were present which would be more fluid than terrestrial tholeiitic lavas and comparable to mare lavas on the moon or archean high mg basalts on earth morphological data and crater counts derived from the high resolution stereo camera on mars express and other orbiters suggest that the lavas flooded gusev crater at about 3 65 b y and postdate older floor materials such as putative sediments emplaced by ma adim vallis

formation of venusian canali considerations of lava types and their thermal behaviors because liquid water is unstable at present venusian surface conditions the discovery of channels termed canali on venus thousands of kilometers long was not predicted low viscosity lavas that remain fluid for several thousand kilometers are considered to be the canali forming agents possible compositions of venusian canali forming lavas include komatiite and high fe ti lunar type basalts results of analytical and numerical models of these lavas reveal that total cooling is more efficient on venus than on earth suggesting that venusian lavas rapidly form insulating crusts and thus that the canali lavas were essentially tube fed the models also reveal that thermal erosion should be less efficient on venus than on earth suggesting that venusian channels are either the product of mechanical rather than thermal erosion or constructional processes

thermal erosion by laminar lava flows thermal erosion by hot lavas during their laminar flow over cold ground is investigated both theoretically and experimentally an analysis of the steady forced convective heat transfer by a laminar channel flow at large peclet numbers is presented which is used to determine the final steady state erosion velocity as well as the thicknesses and timescales of the associated thermal boundary layers in both the lava and ground the initial transient period involving the growth and remelting of a basal chill layer is also quantified laboratory experiments are described in which hot molten wax flowed over and thermally eroded an underlying bed of solidified wax the experimental observations of chill formation and thermal erosion are found to be in excellent agreement with the theoretical predictions the theory is applied to predict rates of thermal erosion consistent with those observed in recent flows of basaltic lava in hawaii and of carbonatite lava in tanzania

dynamic river channels suggest a long lived noachian crater lake on mars 1 recent images of the noachian age holden northeast crater show spectacular meandering channels that form a complex 150 meter thick lacustrine river delta deposit confined to the northwest margin of the crater we identify 11 major avulsion events in the topmost layer and suggest an avulsion frequency of a few hundred years the meandering nature of the channels and numerous avulsions is incompatible with deposition on an alluvial fan and clearly reflects a complex history of multiple sustained flows assuming an average sedimentation rate of 1mm year we suggest that holden ne crater contained a lake that persisted for at least 150 000 years our analysis is incompatible with this feature being the result of a major bolide impact that would have released a catastrophic flood by groundwater sapping and supports the hypothesis that early mars was both warmer and wetter during the noachian

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

erosion by flowing martian lava new insights for hecates tholus from mars express and mer data 1 we have used new compositional information on martian basaltic rocks from the mars exploration rover spirit and data from new stereo imaging by the high resolution stereo camera hrsc on the mars express orbiter to constrain an existing analytical numerical computer model to assess the potential of martian lavas to form lava channels by erosion of substrate the basaltic rocks studied in gusev crater by spirit have compositions consistent with lavas of higher liquidus temperature and lower dynamic viscosity than terrestrial tholeiitic basalts suggesting that they had a greater potential for turbulent flow and erosion of substrate during flow emplacement than terrestrial basalts more similar to lunar mare basalts we modeled a specific case to determine whether these lavas could have formed part of a 66 km long channel on the martian shield volcano hecates tholus this channel formed on relatively steep slopes 2 8 based on measurements from the hrsc digital terrain model our results suggest that erosion rates were of the order of tens to hundreds of centimeters day depending on flow rate and ice content of the substrate eruption durations required to erode the hecates channel 100 30 m deep over the first 20 km depth decreasing downstream range from weeks to months which are consistent with the known eruption durations of terrestrial basaltic lavas and the previous modeling of wilson and mouginis mark 2004 any hecates lava channels formed from erosion by lava could have served as conduits for later fluvial activity as recently described by fassett and head 2004 2005

wrinkle ridges stress domains and kinematics of venusian plains wrinkle ridges are nearly ubiquitous landforms on the plains of venus by analogy with similar structures on other planets venusian wrinkle ridges are inferred to trend normal to the direction of maximum principal compression in the crust an inference that is verified by geometrical relationships with positive and negative relief features on venus because plains are the dominant terrain on venus wrinkle ridges provide an excellent opportunity to determine the orientations of shallow crustal principal stress trajectories over most of the planet in most places there are two or more sets of wrinkle ridges and commonly one of these persists over a very large area defining a regional stress domain intersection relationships indicate that these domains differ in age

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

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

terraces and gilbert type deltas in crater lakes in ismenius lacus and memnonia mars paleolacustrine environments have been widely recognized from landform associations on the surface of mars in contrast to paleolakes in more open areas putative crater lakes commonly display well developed sedimentary landforms especially wave formed terraces and gilbert type deltas this study focuses on terraces and deltas of western memnonia and ismenius lacus as on earth these landforms provide important indications of water dynamics and sedimentary processes the putative martian paleolakes must have been active for thousands of years to have permitted the water movement and wave formation necessary to form one or more terraces fan shaped landforms at the mouths of channels entering crater lake areas may indicate various channel water interaction of these gilbert type deltas are particularly informative their presence indicates multiple flooding events whereby the inlet channels conveyed coarse grained sediment to the crater lake both terraces and deltaic progradation indicate that the crater lakes of memnonia and ismenius lacus were active for long time periods at least for thousands of years during the post heavy bombardment period of the later martian history the unequivocal presence of standing bodies of water of relatively long durations indicates that climatic settings very different from those prevailing today must have occurred at least locally and temporarily during parts of the martian planetary history

geology of the gusev cratered plains from the spirit rover transverse 1 the cratered plains of gusev traversed by spirit are generally low relief rocky plains dominated by impact and eolian processes ubiquitous shallow soil filled circular depressions called hollows are modified impact craters rocks are dark fine grained basalts and the upper 10 m of the cratered plains appears to be an impact generated regolith developed over intact basalt flows systematic field observations across the cratered plains identified vesicular clasts and rare scoria similar to original lava flow tops consistent with an upper inflated surface of lava flows with adjacent collapse depressions crater and hollow morphometry are consistent with most being secondaries the size frequency distribution of rocks 0 1 m diameter generally follows exponential functions similar to other landing sites for total rock abundances of 5 35 systematic clast counts show that areas with higher rock abundance and more large rocks have higher thermal inertia plains with lower thermal inertia have fewer rocks and substantially more pebbles that are well sorted and evenly spaced similar to a desert pavement or lag eolian bed forms ripples and wind tails have coarse surface lags and many are dust covered and thus likely inactive deflation of the surface 5 25 cm likely exposed two toned rocks and elevated ventifacts and transported fines into craters creating the hollows this observed redistribution yields extremely slow average erosion rates of 0 03 nm yr and argues for very little long term net change of the surface and a dry and desiccating environment similar to today s since the hesperian or 3 ga

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

development of lava tubes in the light of observations at mauna ulu kilauea volcano hawaii during the 1969 1974 mauna ulu eruption on kilauea s upper east rift zone lava tubes were observed to develop by four principal processes 1 flat rooted crusts grew across streams within confined channels 2 overflows and spatter accreted to levees to build arched roofs across streams 3 plates of solidified crust floating downstream coalesced to form a roof and 4 pahoehoe lobes progressively extended fed by networks of distributaries beneath a solidified crust still another tube forming process operated when pahoehoe entered the ocean large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone these littoral lava tubes formed abruptly in contrast to subaerial tubes which formed gradually all tube forming processes were favored by low to moderate volume rates of flow for sustained periods of time tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption tubes transport lava efficiently once formed the roofs of tubes insulate the active streams within allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature thus the flows can travel greater distances and spread over wider areas even though supply rates during most of 1970 1974 were moderate ranging from 1 to 5 m3 s large tube systems conducted lava as far as the coast 12 13 km distant where they fed extensive pahoehoe fields on the coastal flats some flows entered the sea to build lava deltas and add new land to the island the largest and most efficient tubes developed during periods of sustained extrusion when new lava was being supplied at nearly constant rates tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano we conclude therefore that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes

hydrogeologic evolution of gale crater and its relevance to the exobiological exploration of mars abstract the presence of an amazonian impact crater lake in the noachian crater gale located in the aeolis northwest subquadrangle of mars is indicated by evidence from young floor deposits streamlined terraces layers and channels observed on the central sedimentary deposit evidence for the filling of this lake by two processes is described a the drainage of the aquifer in the aeolis mensae region supported by extended mass wasting and rim sliding in the crater at the contact with the mensae and b the overspilling of the northern rim by an amazonian south transgression of the elysium basin this last hypothesis is supported by hydrologic features such as channels and channel like depressions north of the crater and by the crescent like shape of the central sedimentary deposit the presence of an impact melt sheet and uplifted central peak may have also generated hydrothermal activity including an early crater lake shortly after the formation of the crater in the noachian period with time decreasing heat flux and changing climates gale may have experienced transitions in aqueous environments from warm and wet to cold and ice covered water that could have provided suitable oases for various communities of microorganisms preservation of the biological and climatic record may have been favored in this paleolacustrine environment which probably occured episodically over two billion years

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

duration of the ma adim vallis gusev crater hydrogeologic system mars abstract ma adim vallis and gusev crater aeolis subquadrangle of mars formed a complex hydrogeologic system through time crater statistics over five geologic units coupled with morphologic and geologic observations show that this system was active over a period ranging from 0 7 to about 2 billion years these results make the floor of gusev crater one of the most prominent martian depositional features the last aqueous sedimentary deposition could have occurred during early amazonian

a case for ancient evaporite basins on mars observations indicate that a martian analog to the earth s salt pans and saline lakes of arid regions may have existed in crater basins during mars early noachian epoch terraced and channelized crater basins point to ponding of surface water as well as possible prolonged and evolving base levels in addition supportive evaporite basin analogs are offered for three other morphologic features of martian crater basins an evaporite basin model for crater basins on mars has major implications for the mechanical chemical and even biological processes that potentially have operated in mars past and represent a spectrum of potential mineral resources

evidence from the mars express high resolution stereo camera for a frozen sea close to mars equator it is thought that the cerberus fossae fissures on mars were the source of both lava and water floods two to ten million years ago evidence for the resulting lava plains has been identified in eastern elysium but seas and lakes from these fissures and previous water flooding events were presumed to have evaporated and sublimed away here we present high resolution stereo camera images from the european space agency mars express spacecraft that indicate that such lakes may still exist we infer that the evidence is consistent with a frozen body of water with surface pack ice around 5 degrees north latitude and 150 degrees east longitude in southern elysium the frozen lake measures about 800 x 900 km in lateral extent and may be up to 45 metres deep similar in size and depth to the north sea from crater counts we determined its age to be 5 2 million years old if our interpretation is confirmed this is a place that might preserve evidence of primitive life if it has ever developed on mars

an igneous origin for features of a candidate crater lake system in western memnonia mars the association of channels inner terraces and delta like features with martian impact craters has previously been interpreted as evidence in favor of the past existence of crater lakes on mars however examination of a candidate crater lake system in western memnonia suggests instead that its features may have formed through igneous processes involving the flow and ponding of lava accumulations of material in craters and other topographic lows throughout much of the study region have characteristics consistent with those of volcanic deposits and terraces found along the inner flanks of some of these craters are interpreted as having formed through drainage or subsidence of volcanic materials channels previously identified as inlets and outlets of the crater lake system are interpreted instead as volcanic rilles these results challenge previous interpretations of terrace and channel features in the study region and suggest that candidate crater lakes located elsewhere should be reexamined

emplacement of the most recent lava flows on hualālai volcano hawai i a detailed field and petrologic study of the ca 1800 a d flows at hual lai volcano documents at least two eruptive episodes the hu ehu e flow field ending in 1801 and the ka p lehu flow several decades earlier the morphology and stratigraphy of the ka p lehu flow require an emplacement duration of several days to weeks based on a comparison with recent eruptive activity at mauna loa volcano the eruption cannot have occurred at the anomalously high rate 104 105 m3 s proposed by previous workers the hummocky flow surface of the later phase of the hu ehu e eruption suggests a duration of months based on a comparison with recent eruptive activity at k lauea volcano although none of the ca 1800 flows show evidence for extraordinarily fast emplacement or unusual fluid rheologies both flows show unusual features the abundant xenoliths for which the ka p lehu flow is famous were transported in numerous episodes of deposition and remobilization during which they eroded the channel systems through which they traveled lava transport in proximal and medial regions of both flow fields was probably through lava tubes as evidenced by preserved tubes and by the prevalence of p hoehoe lined channels that require thermally efficient transport of lava over great distances both flows also show abundant evidence for re occupation of older cones and lava tubes a characteristic that may typify infrequent eruptions of older volcanic systems although lava flows from hual lai volcano do not show anomalous eruptive behavior they pose a substantial hazard for coastal communities of kona

estimation of volcanic eruption conditions for a large flank event on elysium mons mars mars orbiter camera image 5 23 m pixel and topographic data from the mars orbiter laser altimeter data are used to analyze a channel on the upper northern flank of the elysium mons volcano mars we show that this channel is best explained as the product of the thermal erosion of the preexisting surface by a high speed turbulent lava flow fed from a fissure eruption we deduce the volume eruption rate 3400 13 000 m3 s dense rock equivalent the total volume of erupted lava 29 39 km dense rock equivalent and the duration of the activity 40 130 days perhaps significantly the erupted lava volume is essentially identical given the uncertainties in the analysis to the volume of the observed caldera 31 km3 which has implications for volume limited eruptions on mars and potentially for the unusual steep upper slopes of the volcano the eruption that produced the channel appears to have been typical for elysium mons and implies that the other lava channels on the upper flank of the volcano may also have taken 1 4 months to have formed

outflow channels with deltaic deposits in ismenius lacus mars abstract a connected series of outflow channels in the ismenius lacus quadrangle are identified for the first time and characterized using high resolution stereo camera images of mars express the context camera images of mars reconnaissance orbiter and the topography of the mars observer laser altimeter these channels named okavango valles which stretch over 400 km south to north and join the northern plains were identified from braided channels scour groove marks poorly sinuous valleys and depositional landforms discharge rates were estimated to 0 1 5 10 6 m 3 s 1 from analysis of the topography of scour marks pathways of channels segments were extracted from topography showing a unique source at a breached crater rim suggesting overflow from ponded depressions a series of delta fans are observed inside depressions along the channel pathways the presence of these deltas formed in former bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows the similarity of these flows with other outflow channels on mars proves that volcanically related outflows cannot explain all such features in addition this study also shows that catastrophic floods are able to create fan deltas in transient lakes this example has to be taken into account in the interpretation of late stage fans associated with poorly branched valleys and single channels

erosion by flowing lava field evidence erosion of substrate materials by melting or mechanical means has been suggested in active lava flows on earth and other planets although there are many references to lava erosion on earth unambiguous evidence is rare geological relationships commonly cited as evidence of downcutting by lava can be explained without recourse to erosion in order to assess possible erosion by flowing lava we carried out field studies of tube fed basalt flows sheet flows of the columbia river basalt province crb and precambrian komatiites unequivocal evidence for thermal erosion melted dacite substrate was found at the cave basalt lava tube mount st helens for which fluid dynamic analysis indicates laminar flow although erosion was enhanced in areas of locally steep slopes possibly as a result of localized turbulence other lava tubes in our study display strong but inconclusive evidence for erosion komatiite flows display good evidence for erosion of their substrate possibly in a turbulent regime but assessment of the extent of erosion is hampered by limited and disrupted exposures no evidence for thermal erosion was found in the crb our findings suggest that an erosional origin for planetary sinuous rilles and canali would be favored by high reynolds number flows high mass flux low viscosity lava steep slopes and substrates having a lower melting temperature than the lava or low mechanical strength e g regolith

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

origin of periodically spaced wrinkle ridges on the tharsis plateau of mars ridged plains are a major geologic unit on mars and are a predominant unit on the tharsis plateau a region that has undergone uplift extension and extensive shield and flood volcanism these units probably flood volcanic in origin are characterized by landforms classed as wrinkle ridges wrinkle ridges are interpreted to be folds resulting from buckling followed by reverse to thrust faulting flexure fracture a prominent characteristic of many of the wrinkle ridges on mars particularly those in the tharsis ridge system is the periodic nature of their spacing the periodic spacing has been evaluated in six major provinces on the tharsis plateau with regions further divided into domains based largely on variation in ridge orientation the average spacing of the tharsis ridges based on 2934 measurements is 30 km in an effort to account for the periodic nature of the wrinkle ridges the ridged plains material is modeled as both a single member and a multilayer with frictionless contacts that has buckled at a critical wavelength of folding free slip between layers is assumed based on the possible existence of mechanically weak interbeds in the ridged plains sequence separating groups of flows the near surface mechanical structure in the area of ridged plains is approximated by a strong layer or layers overlying a weak megaregolith of finite thickness overlying a strong basement buckling of the ridged plains is assumed to be decoupled from the basement by the weak megaregolith decoupling is enhanced if the megaregolith were water or ice rich at the time of deformation the rheologic behavior of the ridged plains and megaregolith is approximated by a linear elastic and linear viscous material the models are examined for a range in 1 the strength contrast between the ridged plains material and the underlying megaregolith 2 thickness of the ridged plains material 3 thickness of the megaregolith and 4 number of layers the elastic model can explain the observed ridge spacing only if the ridged plains are relatively thick 2400 m with multiple layers n 1 and relatively high contrasts in young s modulus e e0 100 the high e e0 required is possible only if the megaregolith was water rich at the time of deformation over the same range in values of the parameters viscous buckling is much less restricted the viscous model can explain the observed ridge spacing over a wide range in ridged plains thickness 250 m to several kilometers megaregolith thickness number of layers n 1 to 8 and contrasts in viscosity 0 10 in addition viscous buckling is viable if the megaregolith were dry water rich or ice rich at the time of deformation the absence of folds with a cross sectional geometry in the shape of a sinusoid anticline syncline pairs may be the result of initial deformation of the ridged plains material into low amplitude folds in infinitesimal strain followed by plastic yielding in the cores of the anticlines in finite strain initial elastic or viscous buckling coupled with plastic yielding confined to the hinge area followed by the development of reverse to thrust faulting could account for the asymmetric fold geometry of many of the wrinkle ridges

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

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

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

fluvial sedimentary deposits on mars ancient deltas in a crater lake in the nili fossae region 1 new spacecraft observations in the nili fossae region of mars reveal two valley networks 80 and 200 km long that each formed distributary fans as they entered an ancient 40 km diameter impact crater an outlet channel on the eastern crater rim lying at an elevation above the fans suggests these fans formed as subaqueous deltas in a crater lake water flowing in the valley networks entered the crater and deposited the fans and ponded to a maximum depth of about 450 m the lake then overtopped and breached the crater rim incising it and dropping the lake level by 100 m geological evidence combined with the volume of water necessary to fill the crater suggests the duration of flow through this system was prolonged the existence of the deposits described here implies that the early martian environment supported overland flow and ponding of water for an extended period of time

factors influencing lava substrate heat transfer and implications for thermomechanical erosion we develop numerical simulations of basaltic lava flowing laminarly over a basalt substrate in order to examine the details of the lava dynamics and thermal boundary layers and to understand the implications for substrate heating as the initial stage of a larger study of thermomechanical erosion in different planetary environments we aim to understand why erosion occurs on earth why erosion features are not ubiquitous given the high temperatures involved and whether it is a plausible mechanism for the formation of planetary channels such as lunar sinuous rilles and venusian canali here we confine our attention to terrestrial lavas with well known properties and eruption parameters with relatively simple computational fluid dynamic simulations most closely representing tube fed hawaiian basalts for which erosion has been documented we demonstrate the importance of incorporating several key factors in models of lava flow substrate heat transfer which have commonly been neglected in previous treatments by addressing the interaction of the flow dynamics and heat transfer in the lava our work suggests that the development of a temperature gradient in the base of the lava even for undeveloped flow has a significant influence on substrate temperature the sensitivity of the lava substrate interface temperature to the thermophysical properties of the lava and substrate suggests that a delicate balance is required for partial melting to occur thus it might take weeks of continuous flow to initiate partial melting of the substrate at distances of several kilometers from the vent these durations exceed the periods of stability typical of lava flowing in tubes pauses blockages surges and breakouts frequently disrupt the flow however natural irregularities in the flow dynamics or substrate topography might help to initiate and maintain substrate melting on shorter timescales by disturbing the intimately coupled dynamic and thermal boundary layers although a purely thermal mechanism cannot be ruled out our findings support the premise that mechanical erosion may play a key role in reports of erosion based on field evidence

canali type channels on venus some genetic constraints canali type channels on venus are unique because of their great lengths up to 6800 km and nearly constant channel cross sectional shapes along their paths a simple model incorporating channel flow and radiative cooling suggests that common terrestrial type tholeiite lava cannot sustain a superheated and turbulent state for the long distances required for thermal erosion of canali within allowable discharge rates if canali formed mainly by constructional processes laminar tholeiitic flows of relatively high sustained discharge rates might travel the observed distances but the absence of levees would need to be explained an exotic low temperature low viscosity lava like carbonatite or sulfur seems to be required for the erosional genesis of canali

recent aqueous environments in martian impact craters an astrobiological perspective the discovery of gullies and debris aprons raises the question of the existence of aqueous environments on mars in recent geological times and its astrobiological implications three cases of such environments are surveyed at moc high resolution in the e gorgonum chaos and newton and hale craters the regional setting of these craters suggests that the mechanisms of aquifer destabilization flow discharge and gully formation in these three cases result from local geological triggers that can include impact cratering and tectonic processes rather than climate or insolation factor we take as a working hypothesis that microbial life appeared on mars in ancient geological times probably in a geothermal environment but potentially evolving via infrared detection systems to give photosynthetic communities under the selective pressure of energetic solar radiation we hypothesize that some microbial communities could have survived underground in either dormant or active state or that their biomolecules could be preserved either frozen or desiccated in the subsurface beneath the upper oxidized zone we assess the known environmental constraints for life and what type of potential habitats are provided in these three craters by aquifer discharges using comparison with terrestrial analogues and their associated microbial communities these environments include 1 the release of water on a dry crater floor in e gorgonum and the possibility for microorganisms and preserved biomolecules to be flushed out and mixed in with the sediment exposed at the surface 2 the evidence of a recent lacustrine episode in the newton crater with analogy to antarctic dry valley lakes 3 the exposure on the floor of hale crater of material from a regional subsurface that is likely to have retained traces of one of the oldest martian bodies of water recognized to date parker et al 2000 in the argyre basin we show how the water in argyre 3 8 billion years ago gya was likely to have been alterated by hydrothermal processes and how the subsequent formation of the 150 km hale crater on the northern ring of argyre generated hydrothermal pumping this accounts for the anomalously high location of the springs on the crater crests today with respect to the rest of the regional subsurface distribution finally we envision current impact cratering as a factor for destabilizing aquifers on mars today thus creating new environments we analyze the implications of impacts for two geological types of rock units that could harbor traces of life as a result we compare the potential of astrobiological exploration of crater floors rims and ejecta on future missions to mars

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

the stratigraphy of the amenthes region mars time limits for the formation of fluvial volcanic and tectonic landforms abstract we present results of our morphologic and stratigraphic investigations in the amenthes region for which our observations suggest a complex spatial and temporal interrelation between volcanic and possibly water related processes we have produced a series of self consistent geological maps and a stratigraphic correlation chart that show the spatial and temporal distribution of volcanic fluvial and tectonic processes the amenthes region consists of a broad trough like topographic depression that has served as a path for the supply of materials from hesperia planum to isidis planitia it is most likely that hesperia planum and in particular the area north of hesperia planum including tinto vallis palos crater and the surrounding dissected highlands have acted as a source region for materials that were transported into the amenthes trough and farther into the isidis basin the amenthes trough as well as the graben of amenthes fossae were formed after the isidis impact in the noachian and represent likely the oldest features in the amenthes region dendritic valley networks that bear evidence for surface runoff have dissected the highlands adjacent to amenthes planum and within the tinto vallis and palos crater region before 3 7 ga the ridged volcanic plains located near the palos crater and tinto vallis region within amenthes planum as well as within the isidis transitional plains were formed between 3 5 and 3 2 ga and represent the volcanic activity which resulted in the flooding of the amenthes trough the sinuous channel of tinto vallis was formed in the hesperian 3 5 ga and shows characteristics which are consistent with both ground water sapping and igneous processes the palos crater outflow channel was formed nearly at the same time as tinto vallis between 3 5 ga and 3 2 ga and postdates the volcanic flooding of the amenthes trough in the hesperian small valleys 3 4 2 8 ga incised into the ridged plains of amenthes planum appear also within the transitional plains located between the amenthes plains and the isidis interior plains our model ages show that tinto vallis the palos crater outflow channel as well as the small valleys are unlikely formed at the same time and by the same processes as the dendritic valley networks and represent an episode that clearly postdates the volcanic activity

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

meander properties of venusian channels venusian channels which probably are lava channels have meander properties that relate to their mode of formation their channel meanders probably formed in response to flow dynamics as in the case of terrestrial rivers but low sinuosity indicates less developed morphology the meanders generally follow terrestrial river trends for wavelength l to width w ratios suggesting an equilibrium adjustment of channel form slightly higher l w in comparison to terrestrial rivers occurs for venusian channel types other than sinuous rilles the unusually low l w values for some venusian and lunar sinuous rifles probably indicate modification of original meander patterns by erosional channel widening by lavas the slightly larger radius of curvature to wavelength ratios of venusian channels may be attributed to the short time during which the lava channels formed and or they may represent a quasi equilibrium state for the system multiple wavelength meanders of specific venusian channels may have resulted from changes in discharge or from structural control

factors controlling the location of compressional deformation of oceanic lithosphere in the central indian ocean the prominent example of compression of oceanic lithosphere in the central indian ocean south of the indian peninsula does not occur where recent models for the state of stress in the indo australian plate predict maximum horizontal compressive stress the afanazy nikitin seamount group which was erupted in late cretaceous or early tertiary time is centrally located in the region where deformation is best developed we suggest that critical wavelength components in the deflection caused by the emplacement of these seamounts were preferentially amplified when north south directed compression was applied to the northern part of the indo australian plate in the late miocene to test this hypothesis we develop simple one and two dimensional models for compression of a thin elastic plate overlying an inviscid fluid where the plate contains a preexisting deflection the 2 km peak to trough amplitude and 200 km average wavelength characteristics of the broad scale crustal deformation and the observed east west trending pattern of free air gravity anomalies are best matched in the modeling with an applied horizontal compression of 1 5 2 0 1013 n m 1 and a plate with an effective elastic thickness of 10 15 km at the time of compression in addition the lithosphere is particularly susceptible to deformation by horizontal compression if seawater initially filled the deflection due to seamount emplacement but bengal fan sediment fills the additional deflection caused by compression the value of effective elastic thickness determined for the deformed lithosphere is about a factor of 2 less than values obtained from flexure of comparably aged lithosphere beneath seamounts and at trenches 20 30 km we attribute this to plastic yielding at the top and bottom of the lithosphere in response to horizontal loading we determine a north south shortening rate of 1 mm yr 1 from the amplitude of horizontal compression the width of the deformed region and the time interval over which the deformation has occurred this shortening rate is similar to estimates determined from present day plate motion studies

the evolution of the lunar nectaris multiring basin abstract nectaris is an 820 km diameter multiring impact basin located on the near side of the moon the transient cavity is estimated to have been less than 90 km in depth and materials were excavated from a depth of less than 30 km about 2 km thickness of impact melt is believed to line the cavity center the impact event probably took place at about 3 98 0 03 109 years ago nectaris ejecta forms a substantial proportion of the surface materials at the apollo 16 site inter ring plains deposits were deposited after the formation of the nectaris basin the most persuasive origin for the smooth plains is one of extrusives overlain by a thin veneer of ejecta basaltic fragments within apollo 16 samples are believed to have been largely derived from nectaris a titanium rich apollo 16 mare basalt fragment has an age of 3 79 0 05 109 years but although some relatively titanium enriched basalts occur in southern nectaris titanium rich basalts are nowhere seen at the surface of the mare the earliest recognized eruptives appear to be low titanium perhaps vlt basalts found as pyroclastic materials on daguerre and in the gaudibert region the majority of the surface basalts are of intermediate composition possibly similar to apollo 12 basalts and have an age of approximately 3 6 109 years the basalt fill is estimated to have a minimum thickness of 3 km flood style eruptions appear to have been the main form of extrusion mare ridges exhibit a strong north south preferential alignment and appear to postdate basalt emplacement the lack of basin related graben in nectaris is consistent with a thick lithosphere the basin ring structure is best preserved in the southwest and least preserved in the northeast this is believed to result from horizontal variations in the crust and lithosphere thicknesses and from the influence of the preexisting fecunditatis and tranquillitatis basins the ring structure is best preserved where the lithosphere was thickest floor fractured craters within nectaris are intimately associated with the basalt fill both in terms of age and location theophilus ejecta small craters and tycho rays combined with subsidence and mare ridge development were the only modifying influences on nectaris since the termination of basalt eruptions

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

volcanic geology of tyrrhena patera mars tyrrhena patera is a large low relief volcano located in the southern cratered highlands of mars on a proposed ring fracture of the hellas basin the volcano is composed of four or possibly five principal units the oldest and most areally extensive of which are suggested to be ash on the basis of their morphology and erosional characteristics lava flows are observed in a flank flow unit extending from the central caldera to the southwest and apparently cap the summit region models derived from the study of terrestrial pyroclastic flows have been applied to the deposits at tyrrhena patera and indicate that the distribution and lengths of the observed deposits are consistent with an origin by the emplacement of gravity driven ash flows generated by hydromagmatic or magmatic explosive eruptions the hydromagmatic case requires considerable quantities of water 7 5 1016 kg however at volumetric water flow rates determined by other investigators 105 m3 s and calculated from the regional slopes in the hesperia planum region 106 m3 s the amounts necessary could be supplied relatively rapidly in geologic time tyrrhena patera represents the earliest central vent volcanism identified on mars and may reflect a transition from the flood style eruptions which dominated early martian history a hydromagmatic origin for tyrrhena patera is in agreement with suggested climatic changes on mars and may explain the absence of this style of volcanism in later eras alternatively a magmatic origin for tyrrhena patera implies an evolution in the types of magmas produced on mars from hesperian to amazonian time during which the prominent shields in the tharsis region formed

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

the spirit rover s athena science investigation at gusev crater mars the mars exploration rover spirit and its athena science payload have been used to investigate a landing site in gusev crater gusev is hypothesized to be the site of a former lake but no clear evidence for lacustrine sedimentation has been found to date instead the dominant lithology is basalt and the dominant geologic processes are impact events and eolian transport many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration any lacustrine sediments that may exist at this location within gusev apparently have been buried by lavas that have undergone subsequent impact disruption

lava filling of gale crater from tyrrhenus mons on mars abstract gale crater shows infilling of lava of basaltic origin mainly coming from the south via farah vallis using available thermal emission imaging system themis images mars orbiter laser altimeter mola topographic data compact reconnaissance imaging spectrometer for mars crism mineralogical data and geochemical analyses taken in situ by the mars science laboratory msl in different locations of the crater we focused on the possible origin and the main path of the lava that filled gale crater we found that 1 the k ar age of the basaltic rocks on gale s floor is consistent with the age of formation of tyrrhenus mons derived from the southern polar giant impact spgi model 2 the aeolis mensae region does not show evidence for interaction between lava coming from the north elysium mons and lava coming from the south tyrrhenus mons 3 the geomorphological analysis shows that farah vallis is the convergence of a complex network of volcanic channels that can be tracked back to the lava fields of tyrrhenus mons 4 a one dimensional model of lava along the observed path using an adirondrack basalt composition for the substrate shows that lava from tyrrhenus mons is thermally capable of flowing the entire distance to gale before cooling down this evidence is consistent with the lava fill observed at gusev crater

impact crater lakes on mars the robotic search for life on mars centers on identifying accessible environments where the biological catalyst water has existed the formation of large impact craters on mars 65 km diameter may have resulted in the creation of ice covered impact crater lakes which would not freeze for thousands of years even under present climatic conditions water could be supplied from deep confined aquifers penetrated by the impact craters without the need for surface melt water freezing of the lakes is postponed owing to heat from impact generated melt bearing deposits from impact related uplift of hotter rocks from depth and from the latent heat of freezing of a deep crater lake abundant morphologic evidence for ancient crater lakes has not been found in viking images except for craters associated with outflow channels however ice covered crater lakes could have formed and further searches for evidence of these lakes are warranted the lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from mars

evidence for rapid and widespread emplacement of volcanic plains on venus stratigraphic studies in the baltis vallis region geological mapping of the area around baltis vallis the longest 6 800 km canali type channel on venus has led to the determination of stratigraphic relations which appear to be consistent over this entire region comprising 20 x 106 km 2 or 5 of the total surface of venus the most abundant unit in the study area plains with wrinkle ridges pwr consists of two subunits separated by the formation of baitis vailis a feature which is interpreted by most workers to have formed essentially geologically instantaneously the wrinkle ridges deform both subunits of pwr while ridge belts are embayed by the pwr plains consistent age relationships between the pwr subunits wrinkle ridges baltis vallis and ridge belts along the entire 6 800 km channel length is evidence that unit pwr is a real stratigraphic marker unit and not a mosaic of plains emplaced at significantly different times at least in the 5 of the surface of venus comprising the study area the baltis stratigraphic sequence was compared with stratigraphic relations found in earlier studies of thirty six 1 000 x 1 000 km sites randomly distributed over the surface of venus basilevsky and head 1995 and was found to be comparable this supports the interpretation that these stratigraphic units represent generally globally quasi synchronous geologic events rather than the products of geologic activity in different areas of the planet at different times stratigraphic complexes and a number of structures typically formed at several different periods during the observed geologic history this model may correspond to either of two different options for the geologic history of venus 1 the proposed stratigraphic units and equivalent geologic events were generally synchronous over the whole planet or 2 the proposed stratigraphic sequence represents typical sequences of local events which occurred in different places at different times the first option is consistent with the global resurfacing model and the second is consistent with the equilibrium resurfacing model in our previous observations we never saw a case of superposition of one local stratigraphic sequence on another one with repetition of all or part of the sequence of units which would seem to be inevitable at the boundaries of neighboring local activity zones if the second scenario is correct on the basis of this we concluded that the first option consistent with the global resurfacing model agrees better with the observations than the second one however the validity of this conclusion remains tentative for other areas and requires additional testing stratigraphic studies in the area of baltis vallis is a further step in this direction because of the potential for the use of canali type channels as stratigraphic time markers

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

primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of mars five main stages of radial and concentric structures formed around tharsis from the noachian through the amazonian as determined by geologic mapping of 24 452 structures within the stratigraphic framework of mars and by testing their radial and concentric orientations tectonic activity peaked in the noachian stage 1 around the largest center claritas an elongate center extending more than 20 in latitude and defined by about half of the total grabens which are concentrated in the syria planum thaumasia and tempe terra regions during the late noachian and early hesperian stage 2 extensional structures formed along the length of present day valles marineris and in thaumasia with a secondary concentration near warrego vallis radial to a region just to the south of the central margin of valles marineris early hesperian stage 3 radial grabens in pavonis syria ulysses and tempe terra and somewhat concentric wrinkle ridges in lunae and solis plana and in thaumasia sirenum memnonia and amazonis are centered northwest of syria with secondary centers at thaumasia tempe terra ulysses fossae and western valles marineris late hesperian early amazonian stage 4 structures around alba patera the northeast trending alignment of tharsis montes and olympus mons appears centered on alba patera stage 5 structures middle late amazonian represent the last pulse of tharsis related activity and are found around the large shield volcanoes and are centered near pavonis mons tectonic activity around tharsis began in the noachian and generally decreased through geologic time to the amazonian statistically significant radial distributions of structures formed during each stage centered at different locations within the higher elevations of tharsis secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout tharsis

ma adim vallis revisited through new topographic data evidence for an ancient intravalley lake abstract based on a comprehensive study of the recent topographic map usgs mc 23 se i 2119 usgs 1991 topographical map of aeolis plus geomorphic and digital elevation we have constructed a geometric model of ma adim vallis the sedimentary history of the valley was determined by the damming of the valley by two impact craters one by the southern crater over gusev rim and the second located 120 km upstream the presence of an intravalley lake system is inferred from independent sedimentary analysis and from geomorphic evidence for valley benches peripheral and parallel topographic contour intervals of the putative intravalley lake shores suggest that the lake was covered by a thick ice sheet the longitudinal profile of the valley floor shows a peculiar reverse slope located 300 km upstream from the southern gusev crater rim we conclude that this is an accumulation of sedimentary deposits adjacent to the crater rampart which defined the northern boundary of the lake when the water level reached the lowest point of the west bank which is 0 4 km below the top of the rim of gusev crater it began to floor the surrounding plateau as the intravalley lake level raised its ice cover formed a wide lateral bench later this ponded water was funneled into gusev crater through the breaching of the southern gusev rampart by an impact crater the paleolacustrine sediments transported by the lake water that channeled through the rampart debris slope mantled the floor of gusev crater the sublacustrine sediments are promising targets for future missions and of high priority in the search for past life

constraints on the history of open basin lakes on mars from the composition and timing of volcanic resurfacing 1 abundant evidence exists for valley network related fluvial activity near the noachian hesperian transition on mars and areally significant quantities of volcanic ridged plains were emplaced during this period as well thus it is worthwhile to explore the hypothesis that lava water interaction occurred on the surface of mars at this time we analyzed the morphology physical properties composition and surface ages of thirty open basin lakes topographic lows with both an inlet valley and an outlet valley that were also resurfaced by volcanic flows hyperspectral imaging data from the compact reconnaissance imaging spectrometer for mars crism and observatoire pour la mineralogie l eau les glaces et l activite omega instruments indicate that of the 30 basins 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine high calcium pyroxene and low calcium pyroxene an olivine high calcium pyroxene mixture is the most commonly identified mineral assemblage consistent with other hesperian aged volcanic units therefore our mineralogical results for over a third of the open basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties e g surface roughness thermal inertia of the resurfaced open basin lake floors in these 30 examples however no evidence was found for lava water interaction the ages of emplacement derived through counts of superposed craters of all 30 of the open basin lake volcanic resurfacing units show that resurfacing began in the late noachian near the noachian hesperian boundary was concentrated in the hesperian and continued into the early amazonian the lack of geologic features indicative of lava water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing we conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units several of which date to the late noachian early hesperian

observations on basaltic lava streams in tubes from kilauea volcano island of hawai i from 1986 to 1997 the pu u o o kupaianaha eruption of kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10 12 km from vents on the volcano s east rift zone to the ocean within a kilometer of the vent tubes were as much as 20 m high and 10 25 m wide on steep slopes 4 10 a little farther away from the vent some tubes formed by roofing over of lava channels lava streams were typically 1 2 m deep flowing within a tube that here was typically 5 m high and 3 m wide on the coastal plain 1 tubes within inflated sheet flows were completely filled typically 1 2 m high and several tens of meters wide tubes develop as a flow s crust grows on the top bottom and sides of the tubes restricting the size of the fluid core the tubes start out with nearly elliptical cross sectional shapes many times wider than high broad flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting sometimes the tubes began downcutting progressive downcutting was frequently observed through skylights a rate of 10 cm d was measured at one skylight for nearly 2 months

ancient martian volcanoes in the aeolis region new evidence from mola data mars orbiter laser altimeter mola altimetric data confirm the volcanic origin of a noachian aged hilly feature zephyria tholus in the aeolis area of mars similar characteristics shared by at least one nearby topographic high suggest that volcanic activity represented by such features may have been more widespread than previously thought morphological structures and morphometric data for zephyria are consistent with a stratovolcano origin in which the edifice formed by mixed explosive and effusive eruptions and was altered by subsequent flank erosion to produce a distinctive truncated cone with concave upward flanks criteria are outlined to help detect and distinguish the origin of such features in other ancient regions of mars

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

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

geological evolution of the tyras vallis paleolacustrine system mars 1 using the new high resolution stereo camera hrsc data and other martian data sets we reconstructed the hydrological history of an unnamed complex crater in the xanthe terra region the crater hosted a lacustrine basin fed by a dense and centripetal drainage system developed along its inner rim and by the tyras vallis channel where the tyras vallis opens into the crater a prominent delta like feature is visible characterized by a central terrace and two small longitudinal scarps this deposit has been used as sedimentary recorder of the crater lake history and allowed assessment of the overall hydrological evolution two major stands of the water level have been inferred at 700 and 550 m above the crater floor based on the correlation between the morphology and topography of the fan and the crater floor deposits our reconstruction reveals a complex sedimentary evolution of the fan which underwent deltaic and alluvial sedimentation as a result of the different lake water levels and tyras vallis supplies a dominant erosional evolution of the fan delta was determined by the interaction between the fluvial characteristics and basin wave regime wave height analysis and morphological comparison with terrestrial analogues support this hypothesis the lacustrine activity could be chronologically placed between the late noachian and the hesperian the climatic conditions could have allowed the recharge of the regional groundwater system by precipitation and episodic fluvial activity however also heating effects of cratering could have affected the system rejuvenating or accelerating the recharge of the local aquifer

distribution classification and ages of martian impact crater lakes paleolakes in impact craters on mars are characterized at global scale using the viking orbiter data we identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems closed open and lake chain systems we show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity this study provides a catalog of areographic physical and physiographic data for each of the studied impact crater lakes associated with the description of the sedimentary structures observed it also identifies environments where life and or precursors to life could have found favorable conditions to evolve