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

sedimentary resurfacing and fretted terrain development along the crustal dichotomy boundary aeolis mensae mars 1 the evolution of the martian crustal dichotomy boundary which separates the southern cratered highlands from the northern lowland plains by 1 3 km of elevation remains among the fundamental outstanding issues in mars research for a study area at aeolis mensae we show that fretted terrain formed exclusively in a 2 km thick late noachian 3 7 ga sedimentary deposit that overlies the base of an older cratered dichotomy boundary slope in this equatorial study area fretted terrain does not exhibit the debris aprons or lineated valley fills that are attributed to ground ice in otherwise similar midlatitude fretted terrain in arabia terra the massive deposit of fine sand or loess was probably transported from the north by wind and trapped against the precursor dichotomy slope producing a similar initial form to the younger medusae fossae layered materials that occur east of aeolis mensae contemporary with the latest noachian to early hesperian decline in fluvial erosion the fretting process likely initiated as the massive layer s indurated surface was compromised by fracture cratering or collapse into possible voids in these depressions grain impact or contact with water disaggregated the fine sedimentary materials which were then largely deflated by wind the fretting process largely ended when liquid water was no longer widely available for weathering during the early hesperian period although some degradation of the region by aeolian and slope processes has continued to the present

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

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

relaxation of the martian dichotomy boundary faulting in the ismenius region and constraints on the early evolution of mars 1 the martian dichotomy is a global feature separating the cratered southern highlands and smooth northern lowlands parts of the boundary are defined by steep slopes with elevation differences of 2 6 km here we use constraints from the well preserved section of the dichotomy in the ismenius region we study the relaxation of the boundary using both finite element and semianalytical techniques to better constrain the thermomechanical conditions in early mars we argue that the steep slopes are the product of faulting resulting from relaxation of the edge of the boundary by lower crustal flow this relaxation requires that the lower crust must be at least 10 km thick and have a viscosity of 1021 pa s during the first 100 300 myr of relaxation we show that a wet crustal rheology and a thermal gradient of 15 20 k km at 4 ga allows for both the partial relaxation of the martian dichotomy and preservation of long wavelength topography as observed on mars this result is generally consistent with a stagnant lid model of cooling of martian interior the thermal gradient at 4 ga is also consistent with the estimated elastic thickness on early mars our modeling constrains the original slope of the boundary to approximately 2 we cannot constrain the crustal thickness more tightly than the current estimates of 50 100 km on the basis of our semianalytical modeling the relaxation of the boundary can contribute to the general north south slope observed on mars

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

lithospheric flexure and the evolution of the dichotomy boundary on mars 1 the boundary of the martian crustal dichotomy in the eastern hemisphere is one of the most striking topographic features on the planet the long wavelength topography of much of the boundary is expressed by a broad rise and an arched ramp that slopes downward from the southern highlands into the northern lowlands and often ends in a steep scarp lithospheric flexure of the southern highlands for both a continuous and broken plate boundary with the northern lowlands lithosphere is modeled we find that the long wavelength topography of the boundary is best fit by a lithospheric deflection profile of a broken lithosphere for reasonable values of the flexural parameter the lithosphere near the dichotomy boundary may have been weakened by tectonic stress associated with the formation of the crustal dichotomy by subcrustal transport caused by overturn of an early magma ocean

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

forward mechanical modeling of the amenthes rupes thrust fault on mars amenthes rupes overlies one of the largest thrust faults on mars with structural topography accurately measured by mola forward mechanical models successfully predict the surface topography across this large contractional structure the best fitting fault parameters are fault dip angle 25 30 depth of faulting 25 30 km and fault offset 1 5 km these first order results are insensitive to either the offset distribution along the fault or crustal material properties both very shallow e g 15 km and very deep 45 km depths of faulting can be ruled out as can significantly different dips and offset magnitudes amenthes rupes may span the ancient seismogenic lithosphere in the martian noachian highlands implying maximum values at the time of faulting for heat flux of 54 70 mw m 2 and paleogeothermal gradient of 15 20 k km 1

age and origin of the lowlands of mars one of the many significant findings of the mars global surveyor mission is the presence of hundreds of quasi circular depressions qcds observed from high resolution mola topography data their presence has recently been interpreted to reflect a northern lowlands that archive some of the earliest recorded rocks on mars mostly below a veneer of hesperian and amazonian materials here we analyze these data coupled with a recent synthesis of geologic geophysical geomorphic topographic and magnetic information such analysis allows us to suggest a potential plate tectonic phase during the recorded early into middle noachian martian history that transitioned into a monoplate world with episodic magmatic driven activity persisting to present this working hypothesis is based on 1 the observation that the basement of the northern plains is younger than the basement of the southern highlands but older than the material exposures of the cratered highlands suggesting different formational ages for each one of the three geologic time units 2 the observation that parts of the very ancient highland s crust are highly magnetized thus suggesting that most if not all of the formation of the lowlands basement postdates the shut off of the martian dynamo some 4 gyr ago and so allowing hundreds of millions of years for the shaping of the buried lowlands consequently the role of endogenic processes in the earliest geological evolution of mars early perhaps into middle noachian requires reconsideration since mola topographic and mgs magnetic data afford a temporal window sufficient for very early non primordial shaping of the northern lowlands basement

modeling framework for sediment deposition storage and evacuation in the floodplain of a meandering river theory 1 a theory for the movement of suspendible sediment through the floodplain of a simple actively migrating river is developed the floodplain is represented as a series of sediment storage reservoirs each incorporating multiple bends of a river independent models for floodplain sediment deposition and for subsequent removal of sediment by lateral channel migration allow the volume of sediment stored in the floodplain and the associated average floodplain elevation to change over time and down the valley at a given quasi steady discharge deposition depends on a simple one dimensional partition between channel and floodplain discharge and on suspended sediment concentration one size class which varies along the reach depending on lateral supply and floodplain history sediment supply is specified at the upstream end of the reach using a suspended sediment rating curve long term average overbank deposition rates are approximated by weighting multiple steady state solutions using a flow duration curve the channel bed elevation of the system is assumed to be fixed and tributaries are handled using simple lateral source terms the interaction between the submodels is such that under constant boundary conditions the channel evolves toward a state of geomorphic equilibrium where the volume of sediment added to the floodplain by overbank deposition just balances the volume removed by channel migration the model is easily adapted to track conservative suspended sediment tracer material concentration as such material moves through the channel floodplain system

the martian hemispheric dichotomy may be due to a giant impact mars is divided into two fundamentally different geological provinces of approximately hemispherical extent1 3 the more southerly province is heavily cratered contains relatively old geological units and superficially resembles the lunar and mercurian highlands the northern province is relatively lightly cratered and contains younger geological units including extensive plains volcanic edifices and volcanic calderas except for the tharsis and elysium regions and other large volcanoes most of the younger northern province consists of lowlands which lie an average of 3 km below the highlands lowlands occupy about one third of mars they are separated from the highlands by a distinct scarp or by a sloping transitional zone as much as 700km wide in which highland materials have been disrupted and partly replaced by lowland deposits fig 1 the transition is characterized by a variety of landforms unknown on other planets the highlands and lowlands are in isostatic equilibrium across the transitional zone4 no generally accepted explanation for the cause of the highland lowland dichotomy has been proposed although thinning of the lithosph re in the northern hemisphere by internal processes has been suggested5 large impacts which were a feature of early solar system history have also been suggested as an important cause of such early planetary surface heterogeneities3 6 7 subcircular lowlands such as argyre chryse hellas and isidis planitia and the plains south of tharsis occupy previously recognized impact basins8 10 we propose here that the largest expanse of lowlands also results from formation of a large impact basin early in mars history that has profoundly shaped the planet s surface

shock wave equation of state of enstatite shock compression data are reported for hot pressed bamble bronzite en 86 loaded to pressures between 104 and 161 gpa when compared to earlier shock wave data on en 90 at lower pressures and to static compression data our data require the presence of a phase change in p space the data yield two distinct trajectories which cannot be explained by experimental error the higher density data corrected for porosity and a small amount of metallic iron impurity agree with a theoretical en 86 high pressure phase hugoniot calculated from static compression equation of state data for perovskite pv structure silicates when experimental errors and uncertainties in the equation of state parameters are considered all the en86 data can be described by a calculated hugoniot if the first pressure derivative of the mgsio 3 pv bulk modulus is taken as 4 5 1 0 combining the present preferred data with recent shock wave data for single crystal forsterite we find that en 86 is slightly more dense than fo86 at pressures above 110 gpa comparison of the forsterite and enstatite data with the preliminary reference earth model prem lower mantle densities with corrections applied for the higher shock temperatures relative to lower mantle temperatures shows that prem densities are satisfied by olivine or pyroxene stoichiometries with mg mole fractions from 0 82 to 0 90 these values are lower than estimates of 0 90 to 0 95 developed from extrapolating static compression data to lower mantle conditions

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

evidence of debris flow occurrence after wildfire in upland catchments of south east australia abstract numerous reports of flash floods mud torrents and landslides in burnt landscapes of south east australia were only recently linked to debris flows and recognised as a significant process that warrant more detailed investigation this paper provides a systematic documentation of high magnitude erosion events after wildfire in south east australia focusing on small

evidence for and implications of sedimentary diapirism and mud volcanism in the southern utopia highland lowland boundary plain mars abstract several types of spatially associated landforms in the southern utopia planitia highland lowland boundary hlb plain appear to have resulted from localized geologic activity including 1 fractured rises 2 elliptical mounds 3 pitted cones with emanating lobate materials and 4 isolated and coalesced cavi depressions stratigraphic analysis indicates these features are hesperian or younger and may be associated with resurfacing that preferentially destroyed smaller 8 km diameter impact craters based on landform geomorphologies and spatial distributions the documented features do not appear to be specifically related to igneous or periglacial processes or the back wasting and erosion of the hlb scarp we propose that these features are genetically related to and formed by sedimentary mud diapirs that ascended from zones of regionally confined poorly consolidated and mechanically weak material we note morphologic similarities between the mounds and pitted cones of the southern utopia boundary plain and terrestrial mud volcanoes in the absheron peninsula azerbaijan these analogs provide a context for understanding the geological environments and processes that supported mud diapir related modification of the hlb in southern utopia mud diapirs near the elysium volcanic edifice may have resulted in laccolith like intrusions that produced the fractured rises while in the central boundary plain mud diapirs could have extruded to form pitted cones mounds and lobate flows perhaps related to compressional stresses that account for wrinkle ridges the removal of material a few kilometers deep by diapiric processes may have resulted in subsidence and deformation of surface materials to form widespread cavi collectively these inferences suggest that sedimentary diapirism and mud volcanism as well as related surface deformations could have been the dominant hesperian mechanisms that altered the regional boundary plain we discuss a model in which detritus would have accumulated thickly in the annular spaces between impact generated structural rings of utopia basin we envision that these materials and perhaps buried ejecta of utopia basin contained volatile rich low density material that could provide the source material for the postulated sedimentary diapirs thick water rich low density sediments buried elsewhere along the hlb and within the lowland plains may account for similar landforms and resurfacing histories

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

modeling framework for sediment deposition storage and evacuation in the floodplain of a meandering river application to the clark fork river montana 1 a theory for the evolution of a river floodplain and the associated movement of tracer sediment is applied to the case of the upper clark fork river montana whose floodplain is contaminated with tailings derived from historical mining activities deposition of mine tailings raised the elevation of the floodplain which now contributes contaminated sediment to the channel the theory is capable of reproducing the basic aspects of the system s evolution including aggradation of the floodplain during the mining era and subsequent net supply of sediment from floodplain to channel after the cessation of mine input results indicate that the natural removal of tailings from the floodplain could take thousands of years a period longer than is required for the channel to simply rework the tailings the self stabilizing nature of the model results in an evolution toward a new postmine steady state with tailings eventually almost entirely removed from the system

gravity field of mars a 75th degree and order model radiometric tracking data collected by nasa s deep space network dsn for mariner 9 viking 1 and 2 orbiters and mars global surveyor mgs have been analyzed to determine the gravity field of mars the gravity solution mgs75d is a complete spherical harmonics model to degree and order 75 also parts of the solution are the gravitational constants of mars phobos and deimos the significant improvement in the mgs75d mars gravity model is mainly a consequence of globally distributed data set collected from the mgs mapping orbits the use of optimal weighting and constrained least squares solution techniques and improved force and measurement models in the orbit determination process the gravity anomaly map reveals significantly more detail and larger amplitudes than any previous mars gravity map over the major impact and volcanic areas on mars olympus mons remains the largest known gravity anomaly in our solar system and isidis planitia the highest amplitude mascon there are mascons in the hellas argyre and utopia basins valles marineris has distinctive negative anomalies and all volcanic features are positive gravity anomalies over several craters have also been resolved the overall correlation of the mgs75d gravity anomaly map with topography derived from the mars orbiter laser altimeter mola is very high while the polar regions display relatively poor correlation

hemispheres apart the crustal dichotomy on mars the hemispheric dichotomy is a fundamental feature of mars expressed by a physiographic and geologic divide between the heavily cratered southern highlands and the relatively smooth plains of the northern lowlands the origin of the dichotomy which may have set the course for most of the subsequent geologic evolution of mars remains unclear internally driven models for the dichotomy form the lowlands by mantle convection plate tectonics or early mantle overturn externally driven models invoke one giant impact or multiple impacts areal densities of buried basins expressed by quasicircular depressions and subsurface echoes in radar sounding data suggest that the dichotomy formed early in the geologic evolution of mars tectonic features along the dichotomy boundary suggest late stage modification by flexure or relaxation of the highlands after volcanic resurfacing of the northern lowlands subsequent deposition and erosion by fluvial aeolian and glacial processes shaped the present day dichotomy boundary

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

flow resistance and sediment transport by concentrated overland flow in a grassland valley abstract flow resistance and sediment transport data are needed from well vegetated humid environments to evaluate surface wash erosion and channel incision by overland flow in humid environments runoff in valley floors can reach depths of several centimetres but erosion is often limited by dense grass cover intense grazing reduces grass cover but the impacts of this on sediment transport processes are poorly understood we conducted flume experiments in a grassed valley of coastal california to investigate flow resistance and sediment yield under natural conditions and with progressive clipping of grass cover flow resistance has a laminar like relationship with reynolds number but we attribute this to very low velocity beneath submerged stems and not to the state of flow the sediment transport relations provide support for the concept of a threshold shear stress below which erosion is effectively prevented by surface resistance shear stress partitioning suggests that on a densely grassed surface over 90 of flow resistance is exerted on plant stems this effectively prevents sediment transport at boundary shear stresses as high as 1000 1800 dyn cm2 complete clipping of the grass cover reduces the critical shear stress for sediment transport to 11 38 of that under natural conditions continued surface wash erosion and channel initiation are prevented however by strong soil cohesion provided by a dense root mat even with reduction of root density boundary shear stresses of at least 250 430 dyn cm2 are required for channel incision

geologic evolution of the martian dichotomy in the ismenius area of mars and implications for plains magnetization 1 the origin of the martian dichotomy which divides highlands from lowlands is unknown we examine a section of the dichotomy 50 90e defined by steep scarps and normal faults stratigraphy and age relationships preclude the formation of the 2 5 km high boundary via erosion the abrupt disappearance of topographic knobs 300 500 km to the northeast is interpreted as a buried fault alignment of the buried fault with grabens stratigraphy and age determinations using crater counts indicate that the lowland bench is down faulted highlands crust the estimated local strain 3 5 and fault pattern are broadly consistent with gravitational relaxation of a plateau boundary magnetic and gravity anomalies occur on either side of the buried fault admittance analysis indicates isostatic compensation although nonunique a model with a 10 km thick intracrustal block under the lowland bench a 20 km thick block under the plains and an excess density of 200 kg m3 provides a good fit to the isostatic anomaly a good fit to a profile of the magnetic field perpendicular to the dichotomy is produced using uniformly polarized intracrustal blocks 10 20 km thick an intensity of 6 am m a field inclination of 30 and gaps aligned with the isostatic anomalies one interpretation is that high density intrusions demagnetized the crust after dynamo cessation and that low lying magnetized areas could be down faulted highlands crust another model inclination of 30 has magnetized crust beneath the isostatic anomalies separated by gaps the gaps could result from hydrothermal alteration of the crust along fault zones

sediment residence time and connectivity in non equilibrium and transient geomorphic systems abstract growing empirical evidence shows that many geomorphic systems are in transient state or out of equilibrium with respect to the external driving forces the transient state is often related to the dis connectivity of the many constituent parts of geomorphic systems as a result of sediment storage along the sediment flow path from its source to the final sink the response time of geomorphic systems to external changes is thus dependent on the residence time of sediment in various storage compartments here i present a mathematical concept based on reservoir theory to model residence time of sediment using millennial scale sediment budgets the framework sheds light on the limitation of the sediment delivery ratio which is often used as a measure of sediment connectivity in geomorphic systems and provides analytical information on process type pace of sediment flux and connectivity of storage compartments along the sediment cascade the application of the reservoir theory to geomorphic systems under agricultural land use shows that sediment delivery ratios are linked to the virtual velocity of the eroded sediment the time since the onset of agricultural land use and the size of the studied basins with respect to the temporal evolution of sediment storages that temporarily remove sediment from the conveyor belt the framework aims to estimate the sediment residence time in storages which is linked to the effective time scale of disconnectivity reanalysis of a long term empirical sediment budget from central europe reveals that the response to agricultural land use which started 5000 years bp is mainly buffered by the long residence time of sediment on hillslopes in the order of 10 3 years which results in a delayed floodplain aggradation furthermore the framework was applied to paraglacial mountain systems that inherit striking evidences of pleistocene glacial erosion and still recover from the change from glacial to interglacial conditions as a consequence of the reduced lateral and longitudinal connectivity i show that paraglacial response times of sediment flux in mountain headwater in the canadian rocky mountains range in the order of 100 400 ka the results indicate that response times at the transition from glacial to interglacial conditions are much longer than the return interval of the major glaciations causing a transient behavior of mountain headwater basins during interglacial periods the presented reanalysis of millennial scale sediment budgets of agricultural and mountain geosystems provides an integrative framework to link paleo environmental reconstructions and the connectivity of transient geomorphic system to external changes

lineated valley fill and lobate debris apron stratigraphy in nilosyrtis mensae mars evidence for phases of glacial modification of the dichotomy boundary 1 the nilosyrtis mensae region is important among dichotomy boundary fretted terrain outcrops as it provides evidence of overprinting of ancient landscapes by a suite of glacial features providing a composite view of the variety of midlatitude glacial modification processes that can occur during recent martian ice ages on the basis of a series of criteria developed for the identification of a glacial origin for lineated valley fill and lobate debris aprons we interpret stratigraphic topographic and textural relationships between lineated valley fill and lobate debris apron morphological units as evidence of local and regional glacial overprinting of the landscape during the recent amazonian we document 1 stratigraphic relationships between lineated valley fill subunits including the presence of apparently superposed and small scale lobate features 2 the regional integration and flow of lineated valley fill material 3 lineated valley fill degradation and 4 the nature and stratigraphic position of lobate debris aprons these observations suggest multiple phases or episodes of midlatitude valley glacier activity these observations together with those of surface units elsewhere in northern arabia terra interpreted as glacially modified landforms suggest the possibility of midlatitude glacial deposits extending over broad portions of the martian dichotomy boundary within the past several hundred million years

displacement length relations of thrust faults associated with lobate scarps on mercury and mars comparison with terrestrial faults the displacement dand length lof thrust faults associated with lobate scarps on mercury and mars are estimated from topographic and planimetric measurements dranges from 0 29 to 3 58 km for mercurian thrust faults n 10 and from 0 27 km to 2 90 km for martian thrust faults n 13 the d lrelationship between thrust fault populations analyzed on mercury and mars is very similar mercury 6 5 3 2 10 3 mars 5 9 2 0 10 3 and about an order of magnitude lower than terrestrial thrust faults the difference is probably dominated by the contrast in tectonic setting between terrestrial thrust faults and those on mercury and mars the similarity in morphology and the d lrelationship of the mercurian and martian thrust faults may be due to the similarity in mechanical properties of the deformed materials and the acceleration due to gravity of the two planets

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

degree 1 mantle convection and the crustal dichotomy on mars the surface of mars consists of an old heavily cratered and elevated southern hemisphere and younger resurfaced and depressed northern hemisphere a feature often termed the crustal dichotomy the global crustal structure zuber et al 2000 revealed by topography and gravity data from the mars global surveyor spacecraft and the possible late formation of the boundary zone between the hemispheres mcgill and dimitriou 1990 have been proposed to indicate an endogenic origin for the dichotomy however degree 1 mantle convection that is required for any endogenic process to be viable cannot be produced with conventional mantle convection models schubert et al 1990 we have studied the role of radially stratified viscosity on mantle deformation by using rayleigh taylor instability analyses in a spherical shell geometry our analyses reveal that when mantle viscosity is stratified with a weak asthenosphere deformation at long wavelengths is more efficient than that at short wavelengths the weaker the asthenosphere the longer the wavelength at which the deformation is the most efficient a thicker asthenosphere also favors the deformation at long wavelengths both the rayleigh taylor instability analyses and numerical modeling of mantle convection show that degree 1 convection can be produced within the martian mantle provided that the mantle had a weak asthenosphere v500 km thick and v10 2 times weaker than the underlying mantle early in planetary history the degree 1 convection causes preferential heating of one hemisphere that may explain the primary features associated with the dichotomy in crustal structure fl 2001 elsevier science b v all rights reserved

hydrovolcanic tuff rings and cones as indicators for phreatomagmatic explosive eruptions on mars hydrovolcanism is a common natural phenomenon on earth and should be common on mars too since its surface shows widespread evidence for volcanism and near surface water we investigate fields of pitted cones in the nephentes amenthes region at the southernmargin of the ancient impact basin utopia which were previously interpreted as mud volcanoes the cone fields contain pitted and breached cones with associated outgoing flow like landforms based on stratigraphic relations we determined ahesperian or youngermodel age we test the hypothesis of a hydro volcanic origin based on a detailed morphological and morphometrical analysis and an analysis of the regional context an igneous volcanic origin of these cones as hydrovolcanic edifices produced by phreatomagmatic eruptions is plausible several lines of evidence suggest the existence of subsurface water ice the pitted cones display well developed wide central craters with floor elevations below the preeruptive surface their morphometry and the overall appearance are analogous to terrestrial tuff cones and tuff rings mounds that are also observed in the same region resemble terrestrial lava domes the hydrovolcanic interaction between ascending magma and subsurface water and or water ice may explain the formation of the pitted cones although other scenarios such as mud volcanism cannot be ruled out together with the mounds the cones might represent effusive and explosive edifices of amonogenetic volcanic field composed of lava domes tuff rings tuff cones and possibly maars

anomalous tilt of isidis planitia mars 1 we examine several models to account for the contrast between the global northern tilt of mars and the southwest slope of isidis planitia and the putative deuteronilus shoreline surrounding isidis planitia we found the most probable cause for both the tilt of isidis planitia and the deuteronilus shoreline at this location to be a peripheral bulge created by a load in utopia basin using a flexural model it was found that a 12km load resulting in a 6 km deflection in utopia basin could create a peripheral bulge that in distance and magnitude resembles the topographic profile from isidis planitia northeastward into utopia basin

buried mass anomalies along the hemispheric dichotomy in eastern mars implications for the origin and evolution of the dichotomy 1 gravity observations indicate the presence of buried high density material along the hemispheric dichotomy in eastern mars this material is unrelated to present day topography and is probably the result of localized thinning of the crust this thinning may be the result of an epoch of edge driven convection that occurred shortly after the dichotomy formed initiation of edge driven convection requires that lateral variations in lithospheric structure be created on a timescale that is shorter than the conductive cooling time for the lithosphere a few tens of million years at most this timescale cannot be achieved if the dichotomy boundary is created solely by large scale convective flow formation or modification of the boundary by large impact basins such as utopia can create the required lithospheric structure in a geologic instant this suggests that large impacts were important in shaping the dichotomy at least on a regional scale

shock loading experiments on eclogite samples of omphacitic eclogite from fattigau germany were shock loaded to pressures of 18 45 and 59 gpa the recovered specimens were investigated by x ray diffraction experiments and showed all those reflections typical of the well known high pressure phases the unusual appearence of the perovskite structured mgsio3 at the shock loading pressure of 18 gpa is in contrast to results of liu 1980 and could be attributed to strong nonequilibrium processes caused by shock waves

analogue modelling of volcano flank terrace formation on mars of the features that characterize large shield volcanoes on mars flank terraces remain the most enigmatic several competing mechanisms have been proposed for these laterally expansive topographically subtle landforms here we test the hypothesis that horizontal contraction of a volcano in response to the down flexing of its underlying basement leads to flank terracing we performed a series of analogue models consisting of a conical sand plaster load emplaced on a basement comprising a layer of brittle sand plaster atop a reservoir of viscoelastic silicone our experiments consistently produced a suite of structures that included a zone of concentric extension distal to the conical load a flexural trough adjacent to the load base and convexities terraces on the cone s flanks the effects of variations in the thickness of the brittle basal layer as well as in the volume slope and planform eccentricity of the cone were also investigated for a given cone geometry we find that terrace formation is enhanced as the brittle basement thickness decreases but that a sufficiently thick brittle layer can enhance the basement s resistance to loading such that terracing of the cone is reduced or even inhibited altogether for a given brittle basement thickness terracing is reduced with decreasing cone slope and or volume our experimental results compare well morphologically to observations of terraced edifices on mars and so provide a framework with which to understand the developmental history of large shield volcanoes on the red planet

martian plate tectonics the northern lowlands of mars may have been produced by plate tectonics preexisting old thick highland crust was subducted while seafloor spreading produced thin lowland crust during late noachian and early hesperian time in the preferred reconstruction a breakup margin extended north of cimmeria terra between daedalia planum and isidis planitia where the highland lowland transition is relatively simple south dipping subduction occurred beneath arabia terra and east dipping subduction beneath thatsis montes and tempe terra lineations associated with gordii dotsum are attributed to ridge parallel structures while phelegra montes and scandia colles are interpreted as transform parallel structures or ridge fault fault triple junction tracks other than for these few features there is little topographic roughness in the lowlands seafloor spreading if it occurred must have been relatively rapid quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower c 0 4 g gravity of mars the absence of vertical scarps from age differences across fracture zones and the smooth axial topography to the first order the height of vertical scarps across fracture zones does not involve gravity crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity thus the velocity of the rough smooth transition for axial topography also scales inversely with gravity plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age possible plate reorganizations for example the end of spreading through alba patera occur when the ridge axis is far from the trench that is rapid plate motions are inferred to have placed young oceanic crust far from the ridge axis the preferred full spreading rate 900 from the plate pole is 80 mm yr 1 plate tectonics if it occurred dominated the thermal and stress history of the planet a geochemical implication is that the lower gravity of mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the earth age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about mars plate tectonics

structural modeling of lobate scarps in the nw margin of argyre impact basin mars abstract martian lobate scarps are prominent tectonic structures interpreted to be the topographic expression of large thrust faults generated under compression here we present a structural modeling performed on three large lobate scarps ogygis rupes bosporos rupes and phrixi rupes located in the heavily cratered highlands of mars specifically in aonia terra between thaumasia montes and argyre impact basin these lobate scarps formed in the late noachian early hesperian strike parallel to the edge of the thaumasia montes and were generated by ese vergent thrust faults structural analysis of craters deformed by these lobate scarps gives minimum estimates for the faults slip of 1700 3100 m we applied two structural methods in order to constrain the geometry of these thrust faults at depth area balanced cross sections and forward mechanical dislocation modeling obtaining a depth of faulting in this area between 18 and 45 km and dip angles between 23 and 35 these results are consistent with previous studies of lobate scarps on mars the depth of faulting gives an estimation of the depth of the brittle ductile transition at the time of its formation giving a range of depth in which the state of the lithosphere change from brittle to ductile dominated deformation the heat flow values calculated from the obtained depths of the brittle ductile transition range from 25 to 51 mw m 2 we show that the brittle ductile transition depth in aonia terra is set in 18 27 km at a larger distance from the basin center while it is deeper closer to the argyre rim 33 45 km this difference seems to indicate a thickening of the brittle domain under argyre main rim with respect to the external area but attending to regional geology and heat flow values calculated this high value 33 45 km might be an overestimation of the depth of faulting caused by the presence of the crater rim elevation before the formation of the lobate scarps

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

a model for fire induced sediment yield by dry ravel in steep landscapes sediment flux from hillslopes to channels commonly increases following wildfires with implications for the carbon cycle river habitats and debris flow hazards although much of this material is transported via dry ravel existing ravel models are not applicable to hillslopes with gradients greater than the angle of repose which can constitute the majority of mountainous terrain to fill this knowledge gap we develop a continuity model for sediment storage by vegetation dams on steep hillslopes to predict sediment yields following wildfire the maximum volume of sediment stored prior to wildfire is set to be a function of vegetation density the capacity of plants to impound sediment and the contributing hillslope area time is required after fire to establish vegetation and replenish hillslope sediment storage which introduces vegetation regrowth rate soil production rate and fire recurrence interval as important variables that affect ravel yield model results for the san gabriel mountains california predict that sediment yield can increase by several orders of magnitude following fire these results are consistent with field data of ravel yield 30 mm per contributing area of hillslope in 5 months we collected following the 2009 station fire as well as postfire sediment flux recorded by 93 debris basins in contrast to previous work our model shows that heightened postfire sediment yields can be explained by a change in hillslope sediment storage independent of major changes in the soil production rate and landscape form over geomorphic timescales

geomorphological evidence of water level changes in nepenthes mensae mars in the western sector of nepenthes mensae mars there are some geomorphological features that could be related to a standing water sheet in the area such as fluvial terraces deltas and shorelines a detailed analysis of these features reveals two variations in water level probably related to tectonic processes as suggested by the existence of a fissural volcano at this site

lobate scarps and the martian crustal dichotomy landforms reflecting crustal shortening are found in the ancient highlands of the eastern hemisphere of mars these structures referred to as lobate scarps are interpreted to be thrust faults lobate scarps occur near and are oriented roughly parallel to the martian crustal dichotomy a major geologic and topographic boundary that divides the heavily cratered highlands from the relatively smooth featureless northern lowlands the long and short wavelength topography of lobate scarps in the northern terra cimmeria amenthes region have been analyzed using photoclinometry earth based radar altimetry and mars orbiter laser altimeter data the measured relief of lobate scarps in this region ranges from 110 to 1230 m and they occur on gentle regional slopes that dip both toward and away from the dichotomy estimates of the horizontal shortening across the lobate scarps studied range from roughly 0 24 to 2 6 km n 9 assuming fault plane dips of 25 the displacement length d l relationships of thrust faults associated with the lobate scarps are consistent with those observed for terrestrial fault populations the compressional strain in the heavily cratered highlands near the dichotomy determined using the d l data for the lobate scarps is estimated to be 0 17 topographic data indicate that the dichotomy in the northern terra cimmeria amenthes region has a distinct topographic signature the spatial and temporal relationship of the lobate scarps to the boundary suggests that they are related to its formation supporting models for a tectonic origin of the crustal dichotomy

residence times and alluvial architecture of a sediment superslug in response to different flow regimes abstract a superslug was deposited in a basin in the colorado front range mountains as a consequence of an extreme flood following a wildfire disturbance in 1996 the subsequent evolution of this superslug was measured by repeat topographic surveys 31 surveys from 1996 through 2014 of 18 cross sections approximately uniformly spaced over 1500 m immediately above the basin outlet these surveys allowed the identification within the superslug of chronostratigraphic units deposited and eroded by different geomorphic processes in response to different flow regimes over the time period of the study the superslug went through aggradation incision and stabilization phases that were controlled by a shift in geomorphic processes from generally short duration episodic large magnitude floods that deposited new chronostratigraphic units to long duration processes that eroded units these phases were not contemporaneous at each channel cross section which resulted in a complex response that preserved different chronostratigraphic units at each channel cross section having in general two dominant types of alluvial architecture laminar and fragmented age and transit time distributions for these two alluvial architectures evolved with time since the extreme flood because of the complex shape of the distributions they were best modeled by two parameter weibull functions the weibull scale parameter approximated the median age of the distributions and the weibull shape parameter generally had a linear relation that increased with time since the extreme flood additional results indicated that deposition of new chronostratigraphic units can be represented by a power law frequency distribution and that the erosion of units decreases with depth of burial to a limiting depth these relations can be used to model other situations with different flow regimes where vertical aggradation and incision are dominant processes to predict the residence time of possible contaminated sediment stored in channels or on floodplains and to provide insight into the interpretation of recent or ancient fluvial deposits

thrust faults along the dichotomy boundary in the eastern hemisphere of mars 1 mars orbiter laser altimetry mola data have been used to characterize lobate scarps along the dichotomy boundary in the eastern hemisphere of mars these structures are the surface expression of thrust faulting of the southern highlands displacement on the thrust faults is generally less than 1 km except in the case of the amenthes rupes thrust fault where the maximum displacement is on the order of 3 km the ratio of maximum displacement to fault length of the population of thrust faults is 6 2 10 3 n 26 consistent with previous estimates for martian thrust faults based on photoclinometrically derived topography and other planetary thrust fault populations thrust faulting is roughly coincident with late noachian to early hesperian fracturing and normal faulting along the dichotomy boundary this suggests that the formation of the present day dichotomy boundary involved compressional and extensional deformation the long wavelength topography suggests that the dichotomy boundary in the eastern hemisphere may have been formed by flexure of the southern highlands lithosphere lithospheric flexure alone cannot account for the thrust faulting of the highlands along the dichotomy boundary a combination of stresses due to bending erosion and global contraction may have formed the lobate scarp thrust faults

the mola topographic signature at the crustal dichotomy boundary zone on mars mola data collected during the aerobraking hiatus provide good longitudinal sampling of the crustal dichotomy boundary zone in eastern mars and reveal a significant topographic signature associated with the transition from cratered highlands to lowland plains total relief between the two major units is always 2 5 km and sometimes 6 km median elevation differences are about 4 km regional slopes are very low 0 02 in both cratered terrain south and in lowland plains north of the boundary within the transition zone where cratered terrain changes to detached plateaus mesas and knobby terrain slopes are 50 100 times steeper and over a few hundred kilometers average about 1 the topographic signature of the boundary zone is best described as a 2 4 km step function between two nearly flat surfaces similar in slope and amplitude to some terrestrial passive margins this supports previous conclusions of a significant difference in crustal properties thickness composition or both between the lowland plains and cratered terrain and suggests this difference occurs over a relatively short distance of a few to several hundred kilometers

magnitude of global contraction on mars from analysis of surface faults implications for martian thermal history faults provide a record of a planet s crustal stress state and interior dynamics including volumetric changes related to long term cooling previous work has suggested that mars experienced a pulse of large scale global contraction during hesperian time here we evaluate the evidence for martian global contraction using a recent compilation of thrust faults fault related strains were calculated for wrinkle ridges and lobate scarps to provide lower and upper bounds respectively on the magnitude of global contraction from contractional structures observed on the surface of mars during the hypothesized pulse of global contraction contractional strain of 0 007 to 0 13 is indicated by the structures corresponding to decreases in planetary radius of 112 m to 2 24 km respectively by contrast consideration of all recognized thrust faults regardless of age produces a globally averaged contractional strain of 0 011 to 0 22 corresponding to a radius decrease of 188 m to 3 77 km since the early noachian

admittance estimates of mean crustal thickness and density at the martian hemispheric dichotomy 1 admittance estimates from line of sight los acceleration profiles of the mars global surveyor spacecraft are used to constrain the mean crustal thickness and surface density centered on the hemispheric dichotomy from 110 e to 220 e 40 s to 20 n models with uniform crustal properties predict lower than expected bulk crustal densities two layer models with loading only at the surface and the moho produce satisfactory fits to the data the best fit surface density crustal thickness tc and elastic thickness te are 2 5 mg m 3 27 km and 61 km respectively higher elastic thicknesses require lower crustal thicknesses and vice versa the best fit ratio of moho to surface loading f is close to 1 models with no bottom loading f 0 provide a poor fit to the data underestimates in f result in underestimates of both tc and te the surface density is lower than that measured from martian meteorites and by admittance analyses of young volcanoes but is well constrained by the short wavelength admittance values for misfits up to 1 5 times the minimum value and a fixed surface density of 2 5 mg m 3 the ranges of tc te and f are 1 75 km 37 89 km and 0 4 2 6 respectively the apparently compensated nature of the large impact basins has been used to infer a lower bound on southern hemisphere crustal thickness of 45 km if this estimate is correct the likely mean crustal thickness in the area considered is 55 20 km

channel slope reversal near the martian dichotomy boundary testing tectonic hypotheses abstract faults along the martian dichotomy boundary are evidence of tectonic activity which by analogy with terrestrial tectonism may cause changes in or even reversal of fluvial longitudinal profiles in the eastern hemisphere between 30 e and 150 e this tectonic activity has been hypothesized to result from lower crustal flow or from lithospheric flexure for which loading e g by material deposition of the northern lowlands is a possible cause watters 2003a nimmo 2005 the topographic slope changes resulting from these two different mechanisms are distinct and can provide a means for distinguishing between them although other processes may complicate interpretations of reversed longitudinal profiles two fan shaped networks of inverted channels are located near 150 e in the aeolis dorsa region just north of the dichotomy boundary their original flow directions inferred from planform morphology suggest flow to the northeast in contrast to their current longitudinal profiles sloping down to the southwest this contrast indicates slope reversal we investigate the lower crustal flow and flexure mechanisms for slope reversal by testing three different hypotheses 1 lower crustal flow 2 flexure caused by material erosion from the highlands and deposition in the lowlands and 3 flexure caused by highland erosion and deposition in the lowlands plus deposition of the medusae fossae formation in the lowlands we test these three hypotheses by comparing the inferred magnitudes of the slope reversals with predicted slope changes from geophysical models for these processes taking the possibility of non tectonic i e collapse processes into account our results suggest that among these three models the slope reversal is most consistent with the predicted tectonic response to erosion and deposition of highland material in conjunction with deposition of the medusae fossae formation contrary to previous findings our results do not support the mechanism of lateral crustal flow although they do not rule it out because lower crustal flow and erosion may both have been operating but on different time scales the result of this hypothesis testing provides insight into the evolution of the dichotomy boundary and martian crust in this location

influence of the madden julian oscillation on upper tropospheric humidity 1 variations of upper tropospheric humidity uth and cold cloud in the tropics reveal coherent changes that propagate eastward from the indian ocean into the pacific the coherence of uth is high at periods of 30 90 days along the equator near the tropical tropopause uth coherence is large over the equator in the indian ocean and over the subtropics in the central pacific a composite life cycle shows that enhanced uth in the subtropics coincides with two anticyclonic gyres they straddle anomalous cold cloud over the equator as it propagates eastward the enhancement of uth is consistent with anomalously cold temperature which mirrors the anticyclonic gyres those temperature anomalies cancel the height anomaly of the gyres overhead the complex of anomalous uth cold cloud and anticyclonic motion marches eastward across the western pacific until reaching the dateline anomalous convection over the equator then collapses along with the subtropical gyres and enhanced uth accompanying it index terms 3374 meteorology and atmospheric dynamics tropical meteorology 3399 meteorology and atmospheric dynamics general or miscellaneous 3319 meteorology and atmospheric dynamics general circulation 3314 meteorology and atmospheric dynamics convective processes keywords madden julian oscillation upper tropospheric humidity tropical convection

large impact basins and the mega impact origin for the crustal dichotomy on mars the origin of the fundamental crustal dichotomy on mars remains the outstanding unsolved problem in martian geologic evolution the hypothesis that this dichotomy is due to a single giant mega impact early in martian history is tested by comparing the observed number of large impact basins on mars with the number expected from a d 2 distribution this test is based on the assumption that the mega impact borealis basin is the largest member of such a distribution the difference between observed and expected basins is the number of missing basins that might have been obscured by subsequent geologic events if the borealis basin were the largest member of a d 2 impact population there would be a very large number of missing basins on mars 1 larger than 5000 km 10 larger than 2000 km and 40 50 larger than about 1000 km diameter the area occupied by these missing basins allowing for overlap is too large to be hidden by the younger surface units a large population of presently unrecognized large impact basins would have to be located in the well preserved cratered highlands by contrast if chryse is the largest member of a d 2 impact population the more modest number of missing basins could in principle be confined to areas of mars that have been resurfaced or reworked by subsequent geologic processes a possible alternative to the mega impact hypothesis is that the crustal dichotomy is due to the cumulative effects of multiple overlapping large but not giant impacts

deformation induced clinopyroxene fabrics from eclogites abstract clinopyroxene omphacite microfabric studies in eclogites are useful in characterizing the deformation that has affected deeper parts of subduction zones we present the microfabrics and tem structures of four samples representative of the various deformation types known in eclogites the 001 axis tends to be parallel to the lineation while the 010 plane is close to the foliation but these general features undergo strong variations in relation to the shape fabric in strongly lineated samples 010 tends to be spread out in a great circle normal to the lineation whereas 001 is dispersed in the foliation in the case of strongly foliated samples the slip systems identified by tem are 001 100 001 110 and 1 2 110 110 operation of dislocation creep is testified by the presence of dislocations and dislocation walls but this process alone cannot explain all the observed features particularly some aspects of the crystallographic preferred orientation hence other deformation mechanisms must be involved these may be dynamic migration recrystallization by grain boundary migration as well as mass transfer processes this study illustrates that not every crystallographic mineral preferred orientation can be explained by dislocation glide and or twinning processes alone in addition it also demonstrates that eclogite microfabrics can be used to unravel deformation parameters in subduction and or collision zones

topography of the northern hemisphere of mars from the mars orbiter laser altimeter the first 18 tracks of laser altimeter data across the northern hemisphere of mars from the mars global surveyor spacecraft show that the planet at latitudes north of 50 is exceptionally flat slopes and surface roughness increase toward the equator the polar layered terrain appears to be a thick ice rich formation with a non equilibrium planform indicative of ablation near the periphery slope relations suggest that the northern tharsis province was uplifted in the past a profile across ares vallis channel suggests that the discharge through the channel was much greater than previously estimated the martian atmosphere shows significant 1 micrometer atmospheric opacities particularly in low lying areas such as valles marineris

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

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

ancient heat flow crustal thickness and lithospheric mantle rheology in the amenthes region mars surface heat flow calculations for the amenthes region of mars can be independently performed using the depth to the brittle ductile transition and the effective elastic thickness of the lithosphere estimated for the late noachian early hesperian equivalent to an estimated absolute age of 3 6 3 8 ga this along with crustal heat production rates estimated from heat producing elements abundances permits us to put constraints for that particular place and time on both the thermal and mechanical properties of the lithosphere and the crustal thickness the depth to the brittle ductile transition deduced from modeling of the topography of amenthes rupes is 27 35 km and the associated surface heat flow is 26 37 mwm 2 on the other hand the effective elastic thickness in this region is between 19 and 35 km the surface heat flow deduced by considering crustal and lithospheric mantle contributions to the total lithospheric strength as well as wet or dry olivine for lithospheric mantle rheology is 31 49mwm 2 the relatively limited overlap among te andzbdt based heat flowvalues implies a surface heat flowof 31 36mwm 2 with a high fraction originated from crustal heat sources and awet mantle rheology the so obtained local crustal thickness is 43 74 km which suggests an average thickness of 40 75 km for the martian crust for the frequently used crustal density of 2900 kgm 3 our results suggest a crustal thickness of 50 63km for theamenthes region and an average crustal thickness of 45 65 km for mars