lithospheric flexure and the origin of the dichotomy boundary on mars the crustal dichotomy between the ancient highlands of the southern hemisphere and the young appearing northern lowlands is a defining feature of mars in the eastern hemisphere the dichotomy boundary is marked by a prominent scarp and extensional and compressional tectonic features topographic data across the boundary returned from the mars global surveyor indicate lithospheric flexure of the southern highlands the topography of the boundary can be fit by a universal lithospheric deflection profile that corresponds to an elastic thickness of 31 36 km flexure of the southern highlands may be due to late noachian early hesperian vertical loading of the northern lowlands fracturing and normal faulting along the boundary may be in response to bending stresses while thrust faulting may result from a combination of stresses due to flexure erosion and global contraction

hydraulic fracture reopening pressure and the estimation of maximum horizontal stress abstract in hydrofracture stress measurements the magnitude of the maximum horizontal stress s h is commonly estimated from the borehole pressure required to reopen an induced axial crack examination of the processes which govern the borehole pressure history recorded during the reopening cycle of such tests indicates two sources of error in the estimates of s h derived using the conventional method proposed by bredehoeft et al bredehoeft jd wolff rg keys ws and shutter e 1976 colorado geol soc amer bull 87 250 8 the first arises from the failure to include a term arising from pressure penetration into the crack prior to reopening in the force balance acting across the mouth of the induced axial cracks the problem can be remedied by using a modified reopening equation which includes pressure penetration of the crack the second source of error is more problematic and concerns the correct identification of the true reopening pressure from the borehole pressure records analysis of the process of reopening aided by numerical simulations shows that the true reopening pressure is generally less than the apparent i e that detected reopening pressure the discrepancy between true and apparent reopening pressures increases with larger hydraulic compliance of the test equipment the compliance in question refers to that of the fluid volume between the flow meter and the crack mouth s simulation of a pair of 1 m high axial cracks with 2 m residual hydraulic aperture in a 100 mm borehole indicates that the system compliance must be reduced to 5 10 7 m 3 mpa to enable the true reopening pressure to be estimated to better than 10 at flow rate is less than 10 4 m 3 s this is several orders of magnitude less than applies to conventional hydrofracture systems but is attainable for tests in small holes at shallow depth by making relatively minor system modifications tests at greater depth however would seem to require downhole measurement of flow at the packers we validate our assertions with a field test in which reopening pressure was determined mechanically and hydraulically

seismic petrophysics and isotropic anisotropic avo methods for unconventional gas exploration exploration and drilling for natural gas in north america has moved radically away from conventional reservoirs to focus on unconventional reservoirs such as tight gas sands and shales these reservoirs have low porosity and near zero permeability with gas stored in natural fractures and within the matrix porosity economic gas production requires hydraulic fracture stimulation to open connections to existing natural fractures or matrix porosity and successful stimulation depends on the formation s geomechanical brittleness being capable of supporting extensive induced fractures however despite adequate stimulation significant variations exist between wells in expected ultimate recovery eur due to the heterogeneity of these resource plays consequently predicting natural fractures or fracture prone sweet spots is essential to optimize development of such plays

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

numerical model predictions of autogenic fluvial terraces and comparison to climate change expectations terraces eroded into sediment alluvial and bedrock strath preserve an important history of river activity river terraces are thought to form when a river switches from a period of slow vertical incision and valley widening to fast vertical incision and terrace abandonment consequently terraces are often interpreted to reflect changing external drivers including tectonics sea level and climate in contrast the intrinsic unsteadiness of lateral migration in rivers may generate terraces even under constant rates of vertical incision without external forcing to explore this mechanism we simulate landscape evolution by a vertically incising meandering river and isolate the age and geometry of autogenic river terraces modeled autogenic terraces form for a wide range of lateral and vertical incision rates and are often paired and longitudinally extensive for intermediate ratios of vertical to lateral erosion rate autogenic terraces have a characteristic reoccurrence time that scales with the time for relief generation there is a preservation bias against older terraces due to reworking of previously visited parts of the valley evolving spatial differences in bank strength between bedrock and sediment reduce terrace formation frequency and length favor pairing and can explain sublinear terrace margins at valley boundaries age differences and geometries for modeled autogenic terraces are consistent in cases with natural terraces and overlap with metrics commonly attributed to terrace formation due to climate change we suggest a new phase space of terrace properties that may allow differentiation of autogenic terraces from terraces formed by external drivers

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

in situ stress determination from hydraulic injection test data laboratory and field results have shown that the orientation of a hydraulically propagated fracture is not always perpendicular to that of the minimum principal stress but may be influenced by local weakness planes such as preexisting natural fissures the lower the flow rate the stronger the weakness planes influence this observation has led to a new stress determination method based on the measurement of the normal stress supported by fracture planes with various dips and strikes this new method provides means to evaluate the precision of the stress determination and can be applied to situations in which none of the principal stresses is vertical when all the fracture planes are parallel to the borehole axis the method is still applicable if fast flow rate reopening pressures can be measured and if the principal stress directions are assumed to be independent of depth validity of the method is illustrated by analyzing results from two sets of data one of which has been discussed previously in the literature

reconstructing paleolakes in nepenthes mensae mars using the distribution of putative deltas coastal like features and terrestrial analogs abstract nepenthes mensae is an equatorial region situated north of the martian dichotomy northwest of gale crater it is characterized by a nw se oriented belt of interconnected depressions late noachian to early hesperian in age with knobby terrains with residual relief the highlands south of nepenthes mensae middle noachian in age correspond to the licus vallis region which is dissected by drainage networks with valley mouths located along the dichotomy boundary scarp this work presents a detailed geomorphological analysis of ten fan shaped and fifty four coastal like benches identified in nepenthes mensae the combination of detailed mapping morphological and morphometric analyses spatial altitudinal distribution relationships crater counting spectral analysis and comparison with terrestrial analogs suggest that 1 the fan shaped and coastal like benches are likely putative gilbert type deltas and paleoshore platforms respectively and 2 these features may be attributable to paleoshorelines developed along the margins of an ancient inner sea or interconnected paleolakes these findings reveal the important morphogenetic role that liquid water played in the evolution of nepenthes mensae and licus vallis regions during the late noachian early hesperian transition and contribute to contextualize the continuous findings on the environmental and climatic conditions of the nearby gale crater during such time period

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

progressive incision of the channeled scablands by outburst floods the surfaces of earth and mars contain large bedrock canyons that were carved by catastrophic outburst floods reconstructing the magnitude of these canyon forming floods is essential for understanding the ways in which floods modify planetary surfaces the hydrology of early mars and abrupt changes in climate flood discharges are often estimated by assuming that the floods filled the canyons to their brims with water however an alternative hypothesis is that canyon morphology adjusts during incision such that bed shear stresses exceed the threshold for erosion by a small amount here we show that accounting for erosion thresholds during canyon incision results in near constant discharges that are five to ten fold smaller than full to the brim estimates for moses coulee a canyon in the channeled scablands which was carved during the pleistocene by the catastrophic missoula floods in eastern washington usa the predicted discharges are consistent with flow depth indicators from gravel bars within the canyon in contrast under the assumption that floods filled canyons to their brims a large and monotonic increase in flood discharge is predicted as the canyon was progressively incised which is at odds with the discharges expected for floods originating from glacial lake outbursts these findings suggest that flood carved landscapes in fractured rock might evolve to a threshold state for bedrock erosion thus implying much lower flood discharges than previously thought

fill and spill of giant lakes in the eastern valles marineris region of mars the existence of hesperian age 3 7 3 4 ga surface water bodies on mars is a contentious issue often conflicting with favored climate models extensive lakes are proposed to have filled parts of valles marineris during this period yet evidence for their presence and temporal continuity is poorly constrained here we report geomorphic and chronologic evidence for the initiation and demise of a voluminous lake system within the basins of eastern valles marineris we find that independent kilometer deep lakes were present here well after the wetter global climate optimum that characterized the previous noachian epoch 4 1 3 7 ga relative and impact crater chronologies of flood channels emerging from lake basins indicate relatively late lake spillover in the early amazonian ca 3 0 ga drawdown of the lake and cessation of interbasin sedimentation may be recorded by a similar early amazonian ca 3 1 ga crater retention age on the surface of capri mensa a 4 km tall sulfate bearing interior layered deposit the topography data demonstrate that incision of the bedrock barriers between the basins during spillover was driven by a dramatic local base level difference between the lake surface and downstream basin floors we postulate that the lake spillover process created an integrated drainage routing system between a voluminous equatorial water supply and the northern plains basin

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

isrm suggested methods for rock stress estimation part 3 hydraulic fracturing hf and or hydraulic testing of pre existing fractures htpf contents1 introduction 10112 summaryoftestmethods 10123 assumptionsandlimitations 10123 1 hydraulicfracturing hf 10123 2 hydraulictestsonpre existingfractures htpf 10124 apparatus 10134 1 fractureorientationdetectiondevices 10145 personnelquali cation 10146 equipmentperformance 10147 hydraulicfracturingtestprocedure 10148 hydraulic fracturedelineation 10168 1 impressionpackertechnique 10168 2 geophysicalimagingtechnique 10179 obtainingcriticalpressureparametersfromthepressure timerecords 101710 stresscalculations 101810 1 hydraulicfracturing hf 101810 2 hydraulictestsonpre existingfractures 101911 reportingofresults 1019references 1020

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

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

interior channels in martian valley networks discharge and runoff production the highland valley networks are perhaps the most compelling evidence for widespread fluvial activity on mars 3 5 ga however determining the hydrology of these features has been difficult owing to poor image resolution and the lack of available topographic data new orbital imaging reveals 21 late stage channels within valley networks which we use to estimate formative discharges and to evaluate water supply mechanisms we find that channel width and associated formative discharge are comparable to terrestrial valley networks of similar area and relief for 15 narrow channels in basin filling networks likely episodic runoff production rates up to centimeters per day and first order formative discharges of 300 3000 m 3 s are similar to terrestrial floods supplied by precipitation geothermal melting of ground ice would produce discharges 100 times smaller per unit area and would require pulsed outbursts to form the channels in four large valleys with few tributaries wider channels may represent large subsurface outflows or paleolake overflows as these four channels originate at breached basin divides and or near source regions for the catastrophic outflow channels

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

morpho sedimentary and stratigraphic characteristics of the 2000 yigong river landslide dam outburst flood deposits eastern tibetan plateau abstract sedimentary characteristics of landslide dam outburst flood deposits are distinct from those of rainfall flood deposits due to their very high hydraulic energy and sediment concentration while they have been studied well in the geological record investigations of modern outburst flood deposits are relatively rare well preserved flood deposits and landforms caused by the june 2000 landslide dam outburst flood in the yigong river eastern tibet provide an opportunity to evaluate such sedimentological response to a high energy modern event the sedimentary characteristics of boulder bars and channel evolution over c 17 km downstream of the breach were investigated by field survey and remote sensing interpretation the results show that the post flood channel migrated downstream and increased in curvature the bar shape is relatively stable downstream but the bar area shows a fluctuating decrease poorly sorted accumulations composed of massive granular gravels and boulders near the breach indicate sediment rich bedload depositing processes occurred during rapid rising stage flows in contrast there are eddy bars and deposition of fine gravel with horizontally bedded laminations 17 km downstream of the landslide suggesting suspended sediment dominated deposition with a rapid loss of transport capacity comparison with previous hydrodynamic simulations indicates that the rates of the rising stage and the falling stage strongly affect the sedimentary characteristics of boulder bars and slackwater deposits

uncertainty in discriminating lithology in different data domains a major goal of geophysical analysis is to predict the lithologic and fluid content of the subsurface of necessity most of the measurements are conducted remotely using seismic or electromagnetic equipment these remote data should be calibrated with the expected properties of the subsurface principally from well control as a result rock physics is a key component of the process to ensure that the appropriate geophysical response is measured and obtained

in situ stress measurements and regional stress field assessment in the xinjiang candidate area for china s hlw disposal abstract altogether 180 hydraulic fracturing hf in situ stress measurements were conducted in a pre selected area in the xinjiang uygur autonomous region china which is being considered as one of the candidate areas for china s high level radioactive waste hlw repository in situ stress magnitudes and orientations in three sub areas i e yamansu tianhu and aqishan sub areas were obtained from 163 valid measurement points in eight sub vertical boreholes at depths ranging from 17 to 647 m and the variation of the in situ stress components with depth was analyzed the measurement results show that the maximum horizontal stress is larger than the vertical stress within most of the measurement depth ranges indicating that the regional stress field is dominated by tectonic horizontal stress rather than by the overburden stress v within the range of the tested depths the stress field is characterized by h v h where h and h are the maximum and minimum horizontal stresses respectively fracture impression results reveal that the maximum horizontal stress is dominantly oriented in the nee sww direction which is in general in agreement with the orientation of regional tectonic stress field generated from movement of the earth s tectonic plates and is consistent with those interpreted by gps measurements and focal mechanism solutions in addition an abnormal phenomenon in performing stress measurements in one borehole was noticed and the result was discussed using borehole injection test data

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

wave train model for knickpoint migration rivers respond to a drop in their base level by incising the topography the upstream propagation of an incision as usually depicted by a knickpoint migration is thought to depend on several parameters such as the drainage area lithology and the amplitude of the base level drop we first investigate the case of the messinian salinity crisis that was characterized by the extreme base level fall 1500 m of the mediterranean sea at the end of the miocene the response of drainage areas of three orders of magnitude 103 to 106 km2 highlights the dominant role of the drainage area with a square root relationship in controlling the knickpoint migration after a base level fall a compilation of mean rates of knickpoint propagation for time durations ranging from 102 to 107 years displays a similar relationship indicating that successive wave trains of knickpoint can migrate in a river first wave trains linked to the release of the alluvial cover and then wave trains related to the bedrock incision which correspond to the real time response of rivers wave trains with very low retreat rates long lived knickpoints 1 my rather correspond to the response time of regional landscape

martian geomorphology from fractal analysis of drainage networks 1 an alternative approach to conventional planetary terrain analysis is proposed martian terrains represented by topography based on the mars orbiter laser altimetry mola data are represented as a series of drainage basins regardless of the historical presence or absence of actual fluid flow a fractal analysis of each drainage network computationally extracted from an underlying terrain yields a network descriptor a list of four numbers that describes the traits of a network network descriptors are used for a quantitative characterization and classification of martian surfaces we have extracted and analyzed 387 drainage networks from 74 martian locations representing all major epochs and geological units to investigate whether their network descriptors are capable of differentiation between different epochs and geological units we have found that our approach can distinguish morphologically different terrains but only in a statistical sense in particular the method could be used to measure the degree of surface cratering and thus the age of the surface in addition for surfaces that are not heavily cratered the method is capable of distinguishing between different geological units we have found no global trends in the character of martian drainage networks their network descriptors show no systematic dependence on location or elevation our analysis reveals that all noachian surfaces grouped in the npld geological unit have very similar network descriptors regardless of prominence and integration of their visible fluvial features the comparison between statistical description of npld and terrestrial drainage networks shows overall similarities but also some marked differences because of these differences the notion of sustained rainfall on mars during the noachian epoch is inconsistent with our findings but a limited rainfall is compatible with our results

fluvial terraces of the lower susquehanna river abstract fluvial terraces of the lower susquehanna river offer a unique opportunity to investigate the late stage geologic and geomorphic evolution of the u s atlantic passive margin petrography and elevation distinguish and provide a basis for correlation of two groups of terraces the upland terraces and lower terraces through the piedmont newark basin and great valley downstream correlation to dated upper coastal plain and fall zone fluvial deposits relative weathering and soil profile development characteristics establish terrace age upland terraces tg1 tg2 and tg3 middle to late miocene strath terraces 80 to 140 m above the present channel occur only along the piedmont reach they are underlain by unstratified texturally mature quartz dominated roundstone diamictons lower terraces qtg qt1 qt6 pliocene and pleistocene strath and thin aggradational terraces within 45 m of the present channel are underlain by stratified and unstratified texturally and compositionally immature sand gravel and pebbly silt terrace age and longitudinal profiles suggest complex interactions among relative base level long term flexural isostatic processes climate and river grade our model for terrace genesis requires the susquehanna river to attain and maintain a characteristics graded longitudinal profile over graded time for the u s atlantic margin we propose that straths are continually cut along this graded profile during periods of relative base level stability achieved by slow steady isostatic continental uplift acting in concert with eustatic rise change in an external modulating factor such as eustatic fall or climate change results in fluvial incision and subsequent genesis of strath terraces longitudinal profiles of lower susquehanna river terraces which converge at the river mouth diverge through the piedmont and reconverge north of the piedmont contrast with their hypothesized original concave up profiles progressive and cumulative flexural upwarping of the atlantic margin accounts for terrace profile deformation suggesting flexural isostasy as a first order regional deformation mechanism these results offer new interpretations of terrace age correlation and geologic significance that require modification of previous studies suggesting uplifted or anticlinically warped peneplains on the u s atlantic margin

morphometry of small recent impact craters on mars size and terrain dependence short term modification most recent studies of crater morphometry on mars have addressed large craters d 5 km using elevation models derived from laser altimetry in the present work we examine a global population of small 25 m d 5 km relatively well preserved simple impact craters using hirise stereo derived elevation models we find that scaling laws from prior studies of large simple craters generally overestimate the depth and volume at small diameters we show that crater rim curvature exhibits a strong diameter dependence that is well described by scaling laws for d 1 km above this diameter upper rim slopes begin to exceed typical repose angles and crater rims sharpen significantly this transition is likely the result of gravity driven collapse of the upper cavity walls during crater formation or short term modification in addition we identify a tendency for small craters d 500m to be more conical than large craters and we show that the average cavity cross section is well described by a power law with exponent 1 75 neither conical nor paraboloidal we also conduct a statistical comparison of crater subpopulations to illuminate trends with increasing modification and target strength these results have important implications for describing the initial condition of simple crater shape as a function of diameter and geological setting and for understanding how impact craters are modified on the martian surface over time

from basins to rivers understanding the revitalization and significance of top down drainage integration mechanisms in drainage basin evolution abstract the top down drainage basin integration and drainage network evolutionary processes of lake overflow and aggradational spillover or aggradational piracy collectively referred to here as spillover are undergoing a revitalization in the literature to explain aspects of drainage basin evolution and transverse drainage development across the globe spillover processes are commonly unidentified or misidentified as other processes e g piracy capture via headward erosion superimposition antecedence commonly invoked arguments for stream piracy associated with headward erosion are discussed in the context of contemporary research highlighting the inefficiency of this process the term headward erosion in this context is often misconstrued and confused with headward propagating knickpoints in preexisting drainages that are actively evolving this term is therefore misused when discussing basin integration and the establishment of new transverse drainages we propose the term drainage head erosion to rectify this and recommend that headward erosion only be used when referring to real headward erosion when a preexisting stream has headward propagating knickpoints or a knickzone recent investigations have pointed to an engrained paradigm and pedagogical bias as a possible culprit for the lack of recognition of lake overflow and aggradational spillover despite this spillover is common in a variety of terrestrial and extraterrestrial settings including geomorphic and geographic settings ranging from post glacial drainage reorganization to drainage integration processes in extensional tectonic terrains the focus of this manuscript is to provide a summary of these processes as presented in the scientific literature and to highlight the revitalization of spillover in present research with focus on two prominent geomorphic settings where spillover processes commonly occur proglacial environments and extensional terrains like those of the southwestern united states

an examination of in situ rock stress estimation using the kaiser effect abstract when rock cores are loaded in uniaxial compression acoustic emission occurs when the stress reaches a level greater than that which the rock has previously experienced this phenomenon known as the kaiser effect has been used as an indirect method of estimating the in situ stress field in rock masses if the procedure is valid then the kaiser effect method has the advantage that the stress field can be estimated through laboratory tests on rock cores rather than the field drillhole methods of overcoring and hydraulic fracturing however the kaiser effect method is an enigma on the one hand there are good reasons why the method cannot be valid on the other hand there are reports in the literature of it being successfully applied in this paper we explore the variety of geological and mechanical factors involved and report on a case example for the olkiluoto crystalline rock site in western finland we conclude that the kaiser effect method for stress measurement is only likely to be successful if it is supported by key geological and other stress measurement information and if certain procedures are followed as explained in the paper

evidence for ponding and catastrophic floods in central valles marineris mars abstract the valles marineris canyon system of mars is closely related to large flood channels some of which emerge full born from chaotic terrain in canyon floors coprates chasma one of the largest valles marineris canyons is connected at its west end to melas chasma and on its east end to chaotic terrain filled capri and eos chasmata the area from central melas to eos chasmata contains a 1500 km long and about 1 km deep depression in its floor despite the large volumes of groundwater that likely discharged from chaotic terrain in this depression no evidence of related fluvial activity has thus far been reported we present an analysis of the regional topography which together with photogeologic interpretation of available imagery suggests that ponding due to late hesperian discharge of water possibly produced a lake mean depth 842 m spanning parts of the valles marineris depression vmd overflow of this lake at its eastern end resulted in delivery of water to downstream chaos regions and outflow channels our ponding hypothesis is motivated primarily by the identification of scarp and terrace features which despite a lateral spread of about 1500 km have similar elevations furthermore these elevations correspond to the maximum ponding elevation of the region 3560 m simulated ponding in the vmd yields an overflow point at its eastern extremity in eos chasma the neighborhood of this overflow point contains clear indicators of fluvial erosion in a consistent east west orientation

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

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

long river profiles tectonism and eustasy a guide to interpreting fluvial terraces along three rivers at the mendocino triple junction northern california strath cut and fill terraces have formed in response to tectonic and eustatic processes detailed surveying and radiometric dating at multiple sites indicate that lower reaches of the rivers are dominated by the effects of oscillating sea level primarily aggradation and formation of fill terraces during sea level high stands alternating with deep incision during low stands a eustasy driven deposi tional wedge extends tens of kilometers upstream on all rivers tapering to zero thickness this distance is greater than expected from studies of the effects of check dams on much smaller streams elsewhere due in part to the large size of these rivers however the change in gradient is nearly identical to other base level rise studies the depositional gradient is about half that of the original channel middle to upper reaches of each fiver are dominated by the effects of long term uplift primarily lateral and vertical erosion and formation of steep unpaired strath terraces exposed only upstream of the depositional wedge vertical incision at a rate similar to that of uplift has occurred even during the present sea level high stand along rivers with highest uplift rates strath terraces have steeper gradients than the modem channel bed and do not merge with marine terraces at the river mouth consequently they cannot be used to determine altitudes of sea level high stands strath formation is a continuous process of response to long term uplift and its occurrence varies spatially along a river depending on stream power and hence position upstream strath terraces are found only along certain parts of a coastal stream upstream of the aggradational effects of oscillating sea level and far enough downstream that stream power is in excess of that needed to transport the prevailing sediment load for a given size fiver the greater the uplift rate the greater the rate of vertical incision and consequently the less the like lihood of strath terrace formation and preservation

in situ stress measurements and regional stress field assessment of the beishan area china abstract knowledge of the in situ stress field in the rock mass at depth is important to provide stress boundary conditions for underground excavation design stability evaluation and the optimization of ground support systems in the present study in situ stress measurement using hydraulic fracturing method is conducted in the beishan area in gansu province china a preferred candidate site for china s high level radioactive waste repository information on the stress magnitudes and orientations in three sub areas is obtained from 136 measurement points in nine sub vertical boreholes at depths ranging from 30 to 700 m and the distribution characteristics of the in situ stress field is analyzed the pressure time records obtained from the test intervals with pre existing fractures are discussed according to the acoustic borehole televiewer bhtv images the measurement results indicate that the regional stress field is dominated by horizontal stress within most of the measurement depth ranges a piecewise distribution of the principal stresses reveals approximately three stress domains with increasing depth at shallow and medium depths the stress fields are characterized by h h v and h v h respectively where h h and v are maximum horizontal minimum horizontal and vertical stresses respectively with further increase of depth the maximum principal stress changes from horizontal to vertical i e v h h fracture impression results reveal that the maximum horizontal stress is dominantly oriented in the nne nee direction which is in agreement with the orientation of regional tectonic stress field generated from movement of the earth s tectonic plates in addition it is found that the orientations of h are affected by the geological structures significantly

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

updated global map of martian valley networks and implications for climate and hydrologic processes 1 martian valley networks have long been viewed as some of the best evidence of prolonged surface water on mars analysis from viking data showed that valleys were primarily contained on the ancient crust drainage networks were immature and large undissected regions occurred in between individual systems these observations led many to propose that they formed primarily by groundwater processes and limited or no climate change from the present state was required using more recent and higher resolution data sets including visible infrared and topographic data we have manually remapped valleys on a global scale more than eight times as many valleys have been identified on the surface and calculated drainage densities are on average higher by a factor of 2 further regions previously thought to be undissected have significant incision by fluvial processes most of these systems seem to have formed around the noachian hesperian boundary 3 8 3 6 ga minor valley formation continued through the hesperian and into the early amazonian epoch approximately 2 8 ga ago the new data reveal characteristics of sustained precipitation and surface runoff including inner braided channels terraces multiple periods of formation complex network morphology and correlation with other fluviosedimentary features and chloride salts on mars groundwater processes or a transient steam atmosphere generated by impacts played at most a minor role these new results imply that mars had a long lived period or periods of clement conditions toward the end of the noachian epoch that supported a hydrologic cycle and potentially a biosphere

scaling relations for large martian valleys 1 the dendritic morphology of martian valley networks particularly in the noachian highlands has long been argued to imply a warmer wetter early martian climate but the character and extent of this period remains controversial we analyzed scaling relations for the 10 large valley systems incised in terrain of various ages resolvable using the mars orbiter laser altimeter mola and the thermal emission imaging system themis four of the valleys originate in point sources with negligible contributions from tributaries three are very poorly dissected with a few large tributaries separated by long uninterrupted trunks and three exhibit the dendritic branching morphology typical of terrestrial channel networks we generated width area and slope area relationships for each because these relations are identified as either theoretically predicted or robust terrestrial empiricisms for graded precipitation fed perennial channels we also generated distance area relationships hack s law because they similarly represent robust characteristics of terrestrial channels whether perennial or ephemeral we find that the studied martian valleys even the dendritic ones do not satisfy those empiricisms on mars the width area scaling exponent b of 0 7 4 7 contrasts with values of 0 3 0 6 typical of terrestrial channels the slope area scaling exponent ranges from 25 6 5 5 whereas values of 0 3 0 5 are typical on earth the length area or hack s exponent n ranges from 0 47 to 19 2 while values of 0 5 0 6 are found on earth none of the valleys analyzed satisfy all three relations typical of terrestrial perennial channels as such our analysis supports the hypotheses that ephemeral and or immature channel morphologies provide the closest terrestrial analogs to the dendritic networks on mars and point source discharges provide terrestrial analogs best suited to describe the other large martian valleys

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

the role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western san gabriel mountains california bedrock rivers set the pace of landscape adjustment to tectonic and climatic forcing by transmitting signals of base level change upstream through the channel network and ultimately to hillslopes river incision is typically modeled as a monotonic function of bed shear stress or stream power modulated by sediment tools and cover effects but these models do not apply in channels with steep or vertical bedrock reaches due to changes in flow dynamics hydraulic geometry and bed cover here we investigate how such knickzones oversteepened channel reaches often containing waterfalls influence the propagation of slope break knickpoints that separate relict from adjusting topography and thus the response times of landscapes to external forcing we use a conceptual long profile model to explore the consequences of waterfalls and knickzones on channel response and compare predictions to light detection and ranging lidar topography field observations and cosmogenic radionuclide data from big tujunga creek a 300 km2 watershed in the san gabriel mountains california three prominent knickzones along big tujunga creek characterized by numerous waterfalls show contrasting behavior for the upper knickzone waterfalls align with bands of harder rock exposed on adjacent hillslopes and between waterfalls the channel is mantled by large 2 m boulders indicating knickzone retreat is slow compared to predictions of slope break knickpoint retreat from stream power models enhancing the preservation of an upstream relict landscape the middle knickzone shows evidence for both fast and slow knickzone retreat as well as significant deviations from predictions of uniform tributary knickpoint elevations derived from stream power models the lower knickzone is characterized by a waterfall and knickzone within an incised inner gorge that provide evidence of rapid retreat relative to background channel incision overall we find a pattern of decreasing knickzone and waterfall retreat rate with distance upstream of the range front beyond decreases predicted by simple area dependent celerity models our results highlight that waterfalls and knickzones can both enhance and inhibit landscape adjustment leading to divergent controls on the pace of landscape evolution

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

analysis of borehole televiewer measurements in the vorotilov drillhole russia first results abstract in the eurasian part of the world stress map almost the whole region east of the tornquist teisseyre line is terra incognita the closure of this information gap is of fundamental importance to the understanding of the geodynamics of the eurasian continent a detailed analysis of stress induced wellbore breakouts has been performed over a 4 1 km long depth interval in the vorotilov drillhole vgs the borehole is located in the central part of the russian platform right in the center of the vorotilov meteorite impact crater 60 km to the nne of the city of nizni novgorod an ultrasonic borehole televiewer bhtv was used to obtain high resolution acoustical images from the borehole wall with an interactive system for analyzing bhtv data the azimuth and shape of borehole breakouts occurring in the depth range of 1 3 4 8 km were analyzed a statistical analysis of the resulting orientation profile of the breakout azimuths yields an overall direction of the maximum horizontal principal stress s h of n 137 e 15 variations of breakout orientation with depth ranging from a few degrees up to more than 90 are seen on various depth scales the observed stress direction of n 137 e agrees very well with the average s h orientation of n 145 e in central europe if this measurement is taken as representative for the russian platform the stress field in russia is only slightly rotated in comparison to central europe this can possibly be interpreted as indicative for the stress field to be governed by broad scale tectonic forces such as a strong contribution from the forces exerted by the collision zone in the alpine himalayan belt and by the mid atlantic ridge

core disking and its relationship with stress magnitude for lac du bonnet granite abstract core disking is an indicator of elevated stress magnitudes disked cores from boreholes drilled from underground excavations in massive unfractured granite where the stress magnitudes are known with confidence were used to establish a relationship between core disk thickness and the stress magnitude relationships were established for three disk thickness categories 1 thin t d 0 2 2 medium 0 2 t d 0 4 and 3 thick 0 4 t d 2 2 and partial disking the data suggests that core disking initiates when the maximum principal stress normalized to the tensile strength is 6 5

variation of in situ stress regime in coal reservoirs eastern yunnan region south china implications for coalbed methane production knowledge of in situ stress distribution is fundamental for coalbed methane production however it is poorly understood in the eastern yunnan region south china in this study the horizontal maximum shmax and minimum shmin principal stress and vertical stress sv were systematically analyzed for the first time the results indicated that the magnitudes of shmax shmin and sv showed positive correlations with burial depth in general three types of in situ stress fields were determined 1 shmax sv shmin in shallow layers with burial depths less than approximately 600 m 1970 ft below ground level bgl indicating a dominant strike slip faulting stress regime 2 in medium layers approximately 600 800 m 1970 2625 ft bgl the in situ stress state followed multiple relationships suggesting that the in situ stress regime was transformed and 3 sv shmax shmin in deep layers with burial depths greater than approximately 800 m 2625 ft bgl indicating a dominant normal faulting stress regime coal permeabilities obtained from injection falloff well tests showed that they were widely distributed and no obvious relationships were found between coal permeability and effective in situ stress magnitude in the study area the development and orientation of previously generated natural fractures combined with the present day in situ stress distribution controlled the permeability in coal reservoirs differential stress and presence of natural fractures significantly affected the geometry and pattern of hydraulic fractures in addition in the eastern yunnan region locations with relatively deep depths in vertical wells and approximately west northwest east southeast trending horizontal wells suffered high potential of borehole instability because of the high differential stress

topography of mars from global mapping by hrsc high resolution digital terrain models and orthoimages characteristics and performance abstract we report on the results of the mars express high resolution stereo camera hrsc experiment pertaining to one of its major aims mapping the surface of mars by high resolution digital terrain models dtm up to 50 m grid spacing and orthoimages up to 12 5 m resolution we introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation we also address the performance characteristics of the mapping project related to different aspects of internal accuracy accuracy with respect to the global reference system and regional aspects using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data a mean precision of the resulting 3d points of about 12 m is obtained exceeding the mean ground resolution of the stereo images using mars orbiter laser altimeter mola data the hrsc models are firmly tied to the global reference system at the scale of the hrsc dtm grid spacing in the lateral dimension and to within few meters vertically hrsc high resolution dtms are typically generated using a grid size of about 2 times the mean ground resolution but usually not larger than 3 times the mean ground resolution and not smaller than 3 times the precision of the integrated 3d points derived from stereo image analysis statistically every grid cell is based on at least one measured 3d point thus horizontal dtm resolution is well established with regard to the precision and density of the derived 3d points while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued comparison with the dtm derived from mola data allows us to identify specific advancements related to this updated view of martian topography we also address the mapping performance of hrsc in comparison to mola with respect to latitude and to different surface types and morphologies finally comparison with mola highlights typical complementarities of the two different approaches for mapping planetary surfaces

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

canyon formation constraints on the discharge of catastrophic outburst floods of earth and mars catastrophic outburst floods carved amphitheater headed canyons on earth and mars and the steep headwalls of these canyons suggest that some formed by upstream headwall propagation through waterfall erosion processes because topography evolves in concert with water flow during canyon erosion we suggest that bedrock canyon morphology preserves hydraulic information about canyon forming floods in particular we propose that for a canyon to form with a roughly uniform width by upstream headwall retreat erosion must occur around the canyon head but not along the sidewalls such that canyon width is related to flood discharge we develop a new theory for bedrock canyon formation by megafloods based on flow convergence of large outburst floods toward a horseshoe shaped waterfall the model is developed for waterfall erosion by rock toppling a candidate erosion mechanism in well fractured rock like columnar basalt we apply the model to 14 terrestrial channeled scablands washington snake river plain idaho and asbyrgi canyon iceland and nine martian near ares vallis and echus chasma bedrock canyons and show that predicted flood discharges are nearly 3 orders of magnitude less than previously estimated and predicted flood durations are longer than previously estimated from less than a day to a few months results also show a positive correlation between flood discharge per unit width and canyon width which supports our hypothesis that canyon width is set in part by flood discharge despite lower discharges than previously estimated the flood volumes remain large enough for individual outburst floods to have perturbed the global hydrology of mars

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

a large paleolake basin at the head of ma adim vallis mars at 8 to 15 kilometers wide ma9adim vallis is one of the largest valleys in the martian highlands although a groundwater source was previously suggested the channel originates at a spillway in the divide of a 3 000 000 square kilometer closed drainage basin the interior morphology of this source basin including likely shoreline features following topographic contours suggests that ma9adim vallis was created through catastrophic overflow of a 1 100 000 square kilometer highland lake the size constant levels and interior morphology of three regional paleolake basins require a warmer paleoclimate and a long term recharged stable highland water table more than 3 5 billion years ago

tectonic consequences of martian dichotomy modification by lower crustal flow and erosion the martian hemispheric dichotomy shows compressional features a few hundred kilometers south of the dichotomy boundary and contemporaneous extensional features along the boundary two processes that may have contributed to the observed deformation are lateral lower crustal flow and erosion crustal flow causes a decrease in crustal thickness in the south and an increase in the north the result is compressional surface stresses in the highlands and extensional stresses around the dichotomy boundary the magnitude location and timing of the predicted stresses are consistent with the observed tectonic features and strongly suggest that moderate lateral flow occurred for the nominal heat flux and rheology sufficient lateral flow is generated for a mean crustal thickness of 70 km erosion generates extension in the south and compression in the north opposite to what is observed either erosion only resulted in local as opposed to regional distribution of highland material or the rigidity of the lithosphere was sufficiently high at the time of erosion that significant stresses did not develop

global drainage patterns and the origins of topographic relief on earth mars and titan rivers have eroded the topography of mars titan and earth creating diverse landscapes however the dominant processes that generated topography on titan and to some extent on early mars are not well known we analyzed drainage patterns on all three bodies and found that large drainages which record interactions between deformation and erosional modification conform much better to long wavelength topography on titan and mars than on earth we use a numerical landscape evolution model to demonstrate that short wavelength deformation causes drainage directions to diverge from long wavelength topography as observed on earth we attribute the observed differences to ancient long wavelength topography on mars recent or ongoing generation of long wavelength relief on titan and the creation of short wavelength relief by plate tectonics on earth

formation of fluvial hanging valleys theory and simulation 1 although only recently recognized hanging tributary valleys in unglaciated tectonically active landscapes are surprisingly common stream power based river incision models do not provide a viable mechanism for the formation of fluvial hanging valleys thus these disequilibrium landforms present an opportunity to advance our understanding of river incision processes in this work we demonstrate that thresholds apparent in sediment flux dependent bedrock incision rules provide mechanisms for the formation of hanging valleys in response to transient pulses of river incision we simplify recently published river incision models in order to derive analytical solutions for the conditions required for hanging valley formation and use these results to guide numerical landscape evolution simulations analytical and numerical results demonstrate that during the response to base level fall sediment flux dependent incision rules may create either temporary or permanent hanging valleys these hanging valleys form as a consequence of 1 rapid main stem incision oversteepening tributary junctions beyond some threshold slope or 2 low tributary sediment flux response during the pulse of main stem incision thus limiting the tributary s capacity to keep pace with main stem incision the distribution of permanent and temporary hanging valleys results from four competing factors the magnitude of base level fall the upstream attenuation of the incision signal the lag time of the sediment flux response and the nonsystematic variation in tributary drainage areas within the stream network the development of hanging valleys in landscapes governed by sediment flux dependent incision rules limits the transmission of base level fall signals through the channel network ultimately increasing basin response time

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

well bore breakouts and in situ stress the detailed cross sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data we show breakout shapes for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression this work supports the hypothesis that breakouts result from shear failure of the rock where the compressive stress concentration around the well bore is greatest and that breakouts can be used to determine the orientation of the horizontal principal stresses in situ

uncertainty in the maximum principal stress estimated from hydraulic fracturing measurements due to the presence of the induced fracture the classical theory for hydraulic fracturing stress measurements assumes an ideal case with a linear elastic homogenous and isotropic medium and a fracture that reopens distinctly when the minimum tangential borehole stress is exceeded the induced fracture disturbs this ideal picture in several aspects which are important for the evaluation of the maximum horizontal principal stress using the fracture reopening pressure this disturbance can be attributed to the fracture normal stiffness and the initial hydraulic fracture permeability in this paper the hydraulic fracturing reopening test is studied by coupled hydromechanical modeling that takes into account an induced fracture that is incompletely closed the result shows that with realistic equipment compliance the apparent fracture reopening evaluated from the well pressure is close to the magnitude of the minimum horizontal principal stress with little or no correlation to the maximum horizontal principal stress this observation suggests that the determination of maximum principal stress by hydraulic fracturing using the reopening pressure is very uncertain

mosaicking of global planetary image datasets 1 techniques and data processing for thermal emission imaging system themis multi spectral data 1 the mosaicking of global planetary data sets allows for the examination of local regional and global scale processes on all planetary bodies processing techniques that allow us and other users to crate mosaics of tens of thousands of images are documented along with the associated errors introduced by each image processing algorithm these techniques e g non uniformity correction running contrast stretches line and row correlated noise removal and random noise removal were originally developed for the 2001 mars odyssey thermal emission imaging system themis infrared multispectral imager data but can be adapted and applied to other data sets by the alteration of input parameters the techniques for mosaicking planetary image data sets e g image registration blending and normalization are also presented along with the generation of qualitative and quantitative products these techniques are then applied to generate themis daytime and nighttime infrared viking context imager ctx and mars orbiter camera moc visible mosaics using a variety of input and output types at a variety of scales by creating mosaics of the same area using different data sets such as those that illustrate compositional diversity thermophysical properties or small scale morphology it is possible to view the surface of the planet and geologic problems through many different perspectives in addition to the techniques used to create large scale seamless mosaics we also present the themis daytime and nighttime relative temperature global mosaics which are the highest resolution 100m pixel global scale data sets available for mars to date

modeling of knickpoint retreat on the roan plateau western colorado 1 the roan plateau in western colorado constitutes a natural experiment for studying landscape response to a drop in base level late cenozoic incision of the upper colorado river led to elevational isolation of the plateau and initiation of a wave of incision into its southern edge knickpoints oversteepened reaches that contain waterfalls 60 110 m in height mark the upstream extent of this headward propagating wave that this incision has occurred in a laterally extensive well stratified and essentially flat lying bedrock and in an area with relatively uniform climate implies that it should serve as a good test of existing knickpoint propagation models we predict the locations of knickpoints by using a stream power based celerity model in which knickpoint recession rate is a power function of drainage area and is proportional to rock susceptibility to erosion models of the parachute and roan drainages 17 and 16 knickpoints respectively show expected rapid initial knickpoint propagation rates which decline as drainage area decreases stepwise at tributary junctions the modeled positions of knickpoints match well with observed features using a single combination of parameters to model retreat in both drainage basins we compare our celerity model results with past studies and explore how longitudinal profile analysis may be used to derive independently the exponent on drainage area in the celerity model

hydraulics of floods upstream of horseshoe canyons and waterfalls horseshoe waterfalls are ubiquitous in natural streams bedrock canyons and engineering structures nevertheless water flow patterns upstream of horseshoe waterfalls are poorly known and likely differ from the better studied case of a one dimensional linear step because of flow focusing into the horseshoe this is a significant knowledge gap because the hydraulics at waterfalls controls sediment transport and bedrock incision which can compromise the integrity of engineered structures and influence the evolution of river canyons on earth and mars here we develop new semiempirical theory for the spatial acceleration of water upstream of and the cumulative discharge into horseshoe canyons and waterfalls to this end we performed 110 numerical experiments by solving the 2 d depth averaged shallow water equations for a wide range of flood depths widths and discharges and canyon lengths widths and bed gradients we show that the upstream normal flow froude number is the dominant control on lateral flow focusing and acceleration into the canyon head and that focusing is limited when the flood width is small compared to a cross stream backwater length scale in addition for sheet floods much wider than the canyon flow focusing into the canyon head leads to reduced discharge and drying in cases across the canyon sidewalls which is especially pronounced for canyons that are much longer than they are wide our results provide new expectations for morphodynamic feedbacks between floods and topography and thus canyon formation

rapid formation of a modern bedrock canyon by a single flood event deep river canyons are thought to form slowly over geological time see for example ref 1 cut by moderate flows that reoccur every few years in contrast some of the most spectacular canyons on earth and mars were probably carved rapidly during ancient megaflood events quantification of the flood discharge duration and erosion mechanics that operated during such events is hampered because we lack modern analogues canyon lake gorge texas was carved in 2002 during a single catastrophic flood the event offers a rare opportunity to analyse canyon formation and test palaeo hydraulic reconstruction techniques under known topographic and hydraulic conditions here we use digital topographic models and visible near infrared aerial images from before and after the flood discharge measured during the event field measurements and sediment transport modelling to show that the flood moved metre sized boulders excavated 7 m of limestone and transformed a soil mantled valley into a bedrock canyon in just 3 days we find that canyon morphology is strongly dependent on rock type plucking of limestone blocks produced waterfalls inner channels and bedrock strath terraces whereas abrasion of cemented alluvium sculpted walls plunge pools and streamlined islands canyon formation was so rapid that erosion might have been limited by the ability of the flow to transport sediment we suggest that our results might improve hydraulic reconstructions of similar megafloods on earth and mars

hydrographs of a martian flood from a breached crater lake with insights about flow calculations channel erosion rates and chasma growth 1 the elaver vallis channels provide a unique opportunity to develop calibrated hydrographs for a martian flood groundwater filled morella crater until the enclosed lake overtopped the rim confirming that the groundwater potentiometric surface exceeded 1771 m the overtopping flow rapidly breached the crater wall catastrophically drained the lake and eroded a broad scabland and two main channels laser altimeter data were used to calculate a preflood lake volume of 2 216 1012 m3 dam breach methods were used to develop hydrographs of discharge and lake stage over time the peak discharge was in the range of 1 94 107 to 3 51 107 m3 s 1 depending on the underlying breach erosion scenario approximately 95 of the drainable lake volume discharged in 6 4 to 7 5 days the 240 m deep southern channel entirely formed in 1 to 1 7 days indicating a mean erosion rate of 0 10 to 0 17 m min 1 the volume of material eroded from the channels was 0 45 of the flood volume but the actual eroded fraction was probably greater because distant channel reaches were obliterated by the postflood growth of ganges chasma for comparison flow calculations were performed using open channel methods channel energy slopes had to be corrected for a postflood tectonic tilt in the regional surface comparing the hydrographs to the open channel calculations reveals that the northern elaver vallis channel as seen today never flowed bank full or even at half its maximum depth because the implied flows would have exceeded the peak discharges

retreat of a giant cataract in a long lived 3 7 2 6 ga martian outflow channel we describe the evolution of an similar to 600 m deep tributary outflow channel to ares vallis mars high resolution topography image analysis and crater statistics indicate that this tributary canyon developed by the upstream migration of a large similar to 300 m tall cataract during multiple flood events that span similar to 1 b y of mars history 3 7 2 6 ga issuing from hydapsis chaos these floods were initiated at a similar time and occurred over a similar time range to flooding in ares vallis suggesting a potential regional control on flood initiation and chaos formation in addition we provide evidence that cataract retreat and significant incision within the tributary canyon occurred only after a series of downcutting events within ares vallis topography data and crater statistics taken from the floor of ares vallis indicate an similar to 300 m base level drop that coincides temporally with an early amazonian ca 2 6 ga flood event and cataract formation within the tributary canyon the results both confirm the hypothesis of long term multiple flood events within martian outflow channels and demonstrate the influence of base level change on their incision

experimental study of knickpoint and longitudinal profile evolution in cohesive homogeneous material a series of experiments were conducted in homogeneous bedrock to study knickpoint and longitudinal profile evolution knickpoints are created by successive drops in base level which simulate intermittent uplift channel morphology and flow characteristics vary systematically along a knickpoint reach as the knickpoint lip is approached width decreases but depth velocity and bottom shear stress increase as a result knickpoints are rapidly destroyed through the process of 1 knickpoint replacement and 2 subsequent knickpoint inclination knickpoint replacement consists of two morphologically distinct erosional reaches the knickpoint face below the knickpoint lip which decreases in slope and an incising reach above the knickpoint lip which increases in slope knickpoint replacement is a significant process in the evolution of knickpoints in homogeneous bedrock within experimental limits this study supports the notion that knickpoints do not undergo parallel head ward retreat in homogeneous bedrock given intermittent uplift except in those possible cases of extensive and pervasive bedrock jointing only the erosional sediment transport discontinuity above the knickpoint is developed in cohesive sediments below the knickpoint a steep bedrock channel slope low sediment load and rapid decrease in grain size of sediment load preclude development of the aggradational sediment transport discontinuity knickpoint evolution can be characterized by three general models parallel retreat replacement and inclination these models are based on the following criteria within the knickpoint reach 1 relationship between bottom shear stress 0 and critical shear stress needed to initiate motion c 2 nature of the bed load transport discontinuities and 3 spatial variability of bedrock resistance to fluvial erosion

an overview of rock stress measurement methods this paper presents an overview of methods that have been used to estimate the state of stress in rock masses with the emphasis on methods applicable to hard rocks and scandinavia rock stress is a difficult quantity to estimate because the rock stress measuring techniques consist of perturbing the rock measuring displacements or hydraulic parameters and converting the measured quantities into rock stresses there are two main types of method those that disturb the in situ rock conditions i e by inducing strains deformations or crack opening pressures and those that are based on observation of rock behaviour without any major influence from the measuring method the most common methods are briefly described including their application areas and limiting factors

stream terrace genesis implications for soil development genesis of three distinct types of stream terraces can be understood through application of the concepts of tectonically induced downcutting base level of erosion complex response threshold of critical power diachronous and synchronous response times and static and dynamic equilibrium climatic and tectonic stream terraces are major terraces below which flights of minor complex response degradation terraces can form these three types of terraces can be summarized by describing a downcutting aggradation renewed downcutting sequence for streams with gravell bedload by tectonically induced downcutting streams degrade to achieve and maintain a dynamic equilibrium longitudinal profile at the base level of erosion lateral erosion bevels bedrock beneath active channels to create major straths that are the fundamental tectonic stream terrace landform aggradation events record brief reversals of long term tectonically induced downcutting because they raise active channels they may be considered as major the result of climatic perturbations or minor the result of complex response model types of perturbations climatically controlled aggradation followed by degradation leaves an aggradation surface this type of fill terrace tread is the fundamental climatic stream terrace landform aggradation surfaces may be buried by subsequent episodes of deposition unless intervening tectonically induced downcutting is sufficient for younger aggradation surfaces to form below older surfaces raising of the active channel by either tectonic uplift or by climatically induced aggradation provides the vertical space for degradation terraces to form first in alluvial fill and then in underlying bedrock along tectonically active streams these are complex response terraces because they result from interactions of dependent variables within a given fluvial system pauses in degradation to a new base level of erosion and or minor episodes of backfilling lead to formation of complex response fill cut and strath or of fill terraces fill cut terraces are formed in alluvium they are complex response terraces because they are higher than the base level of erosion good exposures and dating are needed to distinguish static equilibrium complex response minor strath terraces from dynamic equilibrium tectonic major straths strath terraces may be regarded as complex response terraces where degradation rates between times terrace tread formation exceed the long term uplift rate for the reach based on ages and positions of tectonic terraces late quaternary global climatic changes control aggradation events and even the times of cutting of major tectonic straths because the base level of erosion can not be attained during times of climatically driven aggradation degradation events most terrace soils form on treads of climatic and complex response terraces aggradation surfaces may provide an ideal flight of terraces on which to study a soils chronosequence each aggradation event is recorded by a single relict soil where tectonically induced downcutting is sufficient to provide clear altitudinal separation of the terrace treads multiple paleosols are typical of tectonically stable regions where younger aggradation events spread alluvium over treads of older climatic terraces pedons on a climatic terrace in a small fluvial system commonly are roughly synchronous variations of soil properties that can be attributed to temporal differences will be minor compared to altitudinally controlled climatic factors climatic terraces of adjacent watersheds also should be roughly synchronous correlatable variations of soil properties that can be attributed to temporal differences will be minor compared to lithologic and climatic factors between different watersheds such generalizations may not apply to basins with sufficient relief that geomorphic responses to climatic changes occur at different and overlapping times and to large rivers whose widely separated reaches are characterized by different response times to climatic perturbations soils on climatic terraces of distant watershedswill not be synchronous if their respective aggradation events occur during full glacial times and interglacial times soils on some complex response terraces may be diachronous within a given fluvial system and typically are diachronous between watersheds

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

insights into surface runoff on early mars from paleolake basin morphology and stratigraphy we present observations on the morphology and stratigraphy of more than 400 paleolake basins on mars we show that there are two distinct classes of martian paleolake basins 1 paleolakes fed by regionally integrated valley networks n 251 and 2 paleolakes fed by isolated inlet valleys not integrated into broader regional drainage systems n 174 we conclude that valley network fed paleolakes primarily formed prior to approximately the noachian hesperian boundary ca 3 7 ga while isolated inlet valley paleolakes primarily formed later in martian history all 174 isolated inlet valley paleolakes are closed basin lakes however there are surprisingly few 31 valley network fed closed basin lakes compared to a large number 220 of valley network fed open basin lakes this observation is consistent with declining levels of fluvial activity over time on the martian surface our results imply that during the era of valley network formation 90 of topographic basins breached by an inlet valley had sufficiently high ratios of water influx to losses to fill overtop and form an outlet valley this conclusion provides an important constraint on the balance between surface runoff production and water losses on early mars that must be satisfied by any model of the early martian climate and hydrologic cycle

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