backthrusting in accretionary wedges backthrusting of the rear of the accretionary wedge arcward over the rocks of the forearc basin is a common aspect of accretionary tectonics an older assumption that backstops of accretionary wedges dip back toward the arc and that accreted material is emplaced below such backstops is contradicted by observations from many active forearcs that indicate 1 backthrusting is common 2 forearc basins are nearly ubiquitous associates of accretionary wedges and 3 forearc basement where imaged appears to diverge from the sedimentary package dipping under the wedge while the overlying sediments are often lifted up against it backthrusting may be favored where relief is high between the crest of the wedge and the surface of the forearc basin because the relief must be supported by shear stress along the backthrust we find ratios of lt lb averaging 2 64 0 8 where lt is the horizontal distance from the crest of the wedge to the front of the toe and lb is the distance from the crest of the wedge to the surface projection of the backthrust this ratio is predicted to increase with total convergence and with sedimentation because the toe undergoes higher deformation rates than the backthrust and sedimentation in the trench favors outbuilding of the toe whereas sedimentation in the forearc basin tends to cancel the gravitational component of the driving stress for the backthrust

crustal balance and crustal flux from shortening estimates in the central andes abstract the central andes of south america form the second largest high elevation plateau on earth extreme elevations have formed on a noncollisional margin with abundant associated arc magmatism it has long been thought that the crustal thickness necessary to support andean topography was not accounted for by known crustal shortening alone we show that this may in part be due to a two dimensional treatment of the problem a three dimensional analysis of crustal shortening and crustal thickness shows that displacement of material towards the axis of the bend in the central andes has added a significant volume of crust not accounted for in previous comparisons we find that present day crustal thickness between 12 s and 25 s is accounted for 10 to 3 with the same shortening estimates and the same assumed initial crustal thickness as had previously led to the conclusion of a 25 35 deficit in shortening relative to volume of crustal material we suggest that the present day measured crustal thickness distribution may not match that predicted due to shortening and substantial redistribution of crust may have occurred by both erosion and deposition at the surface and lower crustal flow in regions of the thermally weakened middle and lower crust

textured dust storm activity in northeast amazonis southwest arcadia mars phenomenology and dynamical interpretation abstractdust storms are mars s most notable meteorological phenomenon but many aspects of their structure and dynamics remain mysterious the cloud top appearance of dust storms in visible imagery varies on a continuum between diffuse hazy and textured textured storms contain cellular structure and or banding which is thought to indicate active lifting within the storm some textured dust storms may contain the deep convection that generates the detached dust layers observed high in mars s atmosphere this study focuses on textured local dust storms in a limited area within northeast ne amazonis and southwest sw arcadia planitiae 25 40 n 155 165 w using collocated observations by instruments on board the mars global surveyor mgs and mars reconnaissance orbiter mro satellites in northern fall and winter this area frequently experiences dust storms with a previously unreported ruffled texture that resembles wide mixed layer rolls in earth s atmosphere a resemblance that is supported by h

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

evolutionary cycles during the andean orogeny repeated slab breakoff and flat subduction tectonomagmatic similarities between the modern chilean flat slab region and pre neogene magmatic episodes suggest that they represent analogues to flat subduction evolutionary patterns in each magmatic suite include i increasing la yb ratios and sr and nd isotopic enrichment through time ii eastward migration of magmatism after periods of transpressional transtensional intra arc deformation and iii subsequent termination and virtual absence of main arc activity for 5 10 myr these patterns may reflect slab shallowing followed by flat subduction and thickening of the overlying crust if repeated they require interchanging episodes of slab steepening increasing convergence rates force slab kinking and eventual failure of the oversteepened slab followed by rebound of the slab tip owing to lack of further slab pull flat subduction and termination of subduction related magmatism rapid subduction leads to shallow overriding of the detached slab fragment eclogitization of the gradually steepening slab tip at depth and subsequent slab pull permits asthenospheric corner flow and subduction related magmatism

the west andean thrust the san ramon fault and the seismic hazard for santiago chile 1 the importance of west verging structures at the western flank of the andes parallel to the subduction zone appears currently minimized this hampers our understanding of the andes altiplano one of the most significant mountain belts on earth we analyze a key tectonic section of the andes at latitude 33 5 s where the belt is in an early stage of its evolution with the aim of resolving the primary architecture of the orogen we focus on the active fault propagation fold system in the andean cover behind the san ramon fault which is critical for the seismic hazard in the city of santiago and crucial to decipher the structure of the west andean thrust wat the san ramon fault is a thrust ramp at the front of a basal detachment with average slip rate of 0 4 mm yr young scarps at various scales imply plausible seismic events up to mw 7 4 the wat steps down eastward from the san ramon fault crossing 12 km of andean cover to root beneath the frontal cordillera basement anticline a range 5 km high and 700 km long we propose a first order tectonic model of the andes involving an embryonic intracontinental subduction consistent with geological and geophysical observations the stage of primary westward vergence with dominance of the wat at 33 5 s is evolving into a doubly vergent configuration a growth model for the wat altiplano similar to the himalaya tibet is deduced we suggest that the intracontinental subduction at the wat is a mechanical substitute of a collision zone rendering the andean orogeny paradigm obsolete

structure and cenozoic kinematics of the eastern cordillera southern bolivia 21 s 1 the eastern cordillera is a main morphotectonic unit of the central andes in southern bolivia it is predominantly composed of ordovician sedimentary rocks as thick as 10 km revision of the ordovician stratigraphy and new structural fieldwork resulted in detailed balanced cross sections improved estimates of crustal shortening and a new kinematic model for the eastern cordillera new estimates of total shortening in the eastern cordillera are up to 95 km 41 44 higher than previous estimates and sufficient to thicken the andean crust to its present state between the eastern foreland and the magmatic arc after initial tertiary uplift at 58 ma first thrusts developed in the middle eocene to early oligocene 40 30 ma exhuming the central part of the eastern cordillera tectonic shortening culminated in late oligocene and early miocene time 25 20 ma when west facing thrust systems developed in the central and western part of the eastern cordillera thrusting terminated in the western part by the end of the early miocene and middle miocene tectonic activity was restricted to minor strike slip faulting in the central part thrusting remained active until the late miocene by 10 ma shortening in the eastern cordillera essentially ceased kinematic fault analyses indicate clockwise rotation of the shortening direction from nne ssw or ne sw in eocene early oligocene time over e w to wnw ese or even nw se in late oligocene to middle miocene time nevertheless wnw ese directed shortening and subvertical extension predominate sinistral oblique motion on many thrusts probably reflects plan view flexural slip in the clockwise rotating southern limb of the bolivian orocline it is proposed that space problems in the oroclinal hinge slowed the rotation there and caused decoupling of the still rotating south limb along ne trending transfer zones

the evolution of deformation and topography of high elevated plateaus 1 model numerical analysis and general results a temperature dependent viscoplastic flow model of continental lithosphere is used to investigate the evolution of deformation and topography of high elevated plateaus such plateaus are products of both continent continent collision tibetan plateau and ocean continent collision the altiplano and develop in the overriding continental plate in this study we emphasize the mechanically simpler case of oceanic collision because it does not involve mass transfer between the two plates the lithosphere is deformed in response to tectonic and buoyancy forces the tectonic forces arise from subduction of an oceanic plate or underthrusting of continental lithosphere that horizontally indents and vertically shears the overriding lithosphere the buoyancy forces arise in response to horizontal density variations and tend to relax existing topography or thick crust the time evolution of the deformation and topography is investigated using a finite element technique that solves for the flow field in the overriding lithosphere the model produces dynamically supported near trench topography and inland mountain topography that is isostatically supported by a thick crust a finite region of localized deformation thick crust and high topography develops only if the model includes a horizontal thermal perturbation or an initially thick crust however only thermally perturbed lithosphere generates a plateau topography the shape and size of the calculated plateau depend on the wavelength of the thermal perturbation grashof number and density contrast between the crust and mantle the time evolution of the deformation shows a significant change in the deformation pattern as the high elevated plateau evolves during early stages compressional deformation of the crust and mantle are localized in the thermally perturbed weak zone at later stages as the crust thickens buoyancy forces of larger magnitude resist further thickening of the crust and the locus of compressional crustal deformation migrates inland this migration does not affect the location of the mantle deformation which remains in the thermally weak region but it is accompanied by a significant shear deformation in the weak lower crust the separation of the crustal locus from the mantle locus of deformation emphasizes the importance of vertically dependent deformation in the formation of high elevated plateaus this demonstrates the limitations of models that ignore changes of deformation with depth such as plane stress or thin sheet models

relationship between frontal dust storms and transient eddy activity in the northern hemisphere of mars as observed by mars global surveyor we have compiled a catalog of frontal dust storms in the northern hemisphere using mars orbiter camera daily global maps spanning 2 3 martian years of mars global surveyor mgs observations from 1999 to 2003 the most vigorous frontal storms that flush dust to the low latitudes occur in early mid fall and mid late winter away from the northern winter solstice while many streaks are observed in the polar hood during the winter solstice period no frontal dust storms are observed in the vicinity of the north polar region we have also analyzed simultaneous mgs thermal emission spectrometer tes temperature data and found statistically significant negative temperature anomalies associated with frontal storms in the lowest scale height of the atmosphere the geographical and seasonal distributions of temperature standard deviations associated with transient variations agree well with the distributions of frontal storms the correlation deteriorates with increasing altitude suggesting that lower level temperature waves are associated with the frontal dust storms specifically eastward traveling m 3 waves with periods of 2 3 sols appear to be closely related to the development of flushing frontal storms

modeling the influence of sinking anhydrite blocks on salt diapirs targeted for hazardous waste disposal due to the low permeability and high ductility of rock salt many salt diapirs such as those in germany and the netherlands are targeted as long term repositories for disposal of high level radioactive and chemical wastes geophysical and subsurface data show that the gorleben salt diapir which is one of the most extensively investigated diapirs in the world and other salt diapirs of the zechstein formation in germany contain large blocks 80 m thick of high density anhydrite inclusions these blocks which were carried upward by the rising salt are considered to be detached segments of intercalated layers that initially were deposited with the salt results of physical and numerical models presented here show that such detached high density blocks which were entrained and carried upward by the diapir at an earlier stage tend to sink in the late stages of diapiric evolution when the rate of diapiric rise slows down during their descent these high density competent blocks deform by folding and create shear zones at the immediate contact with the less competent salt the descending blocks initiate a secondary internal flow within the salt diapirs they descend and they may deform any repository built within such diapirs which would otherwise be considered as tectonically inactive

high level surfaces plateau uplift and foreland development bolivian central andes newly dated tertiary strata in the bolivian central andean plateau and synthesis of the tertiary record in the adjacent subandean fold thrust belt constrain the age of deformation in both regions age of deformation within the plateau is determined by dated crosscutting relations associated with a regionally extensive high level surface known as the san juan del oro surface new 40 ar 39 ar dates on undeformed strata above the high level surface preclude significant upper crustal shortening within the eastern cordillera after 10 ma tertiary strata within the adjacent subandean region demonstrate that formation of the fold thrust belt occurred after 10 ma on the basis of these data we propose a two stage model of late cenozoic andean growth that links plateau uplift to the development of the fold thrust belt in the first stage early plateau uplift occurred in response to widespread compressional deformation of the plateau eastern cordillera and altiplano during the second stage beginning after 10 ma upper crustal deformation within the plateau terminated and the subandean fold thrust belt developed crustal scale eastward thrusting along the eastern margin of the eastern cordillera drove subandean folding and thrusting the eastern cordillera served as the bulldozer for the deforming subandean wedge

dust storms originating in the northern hemisphere during the third mapping year of mars global surveyor abstract data from the third mars global surveyor mgs mapping year my 26 2003 2005 are used to investigate dust storms originating in the northern hemisphere flushing dust storms which originate as frontal dust storms at the northern polar vortex edge and propagate southward through topographic channels are observed immediately before and after a quiescent period that occurs around the northern winter solstice 240 l s 300 both the pre and post solstice active periods can be further divided into two sub periods the most vigorous of these flushing storms occurred during l s 210 220 and l s 310 320 the lifted dust crossed the equator and accumulated in the southern hemisphere these major dust storms enhanced the hadley circulation and suppressed the lower level baroclinic eddies in the northern mid and high latitudes the 2 3 sol wave number m 3 traveling waves show the best correlation with flushing dust storms and can combine with other wave modes to produce storm tracks and fronts within individual sub periods

controls on the shape and kinematics of the central andean plateau flanks insights from numerical modeling abstract the flat surface of orogenic plateaus requires a weak detachment at the base of the crust that prevents the formation of large wavelength topography in the centre of the orogen and decouples the deformation of crust and mantle this study uses numerical distinct element simulations of plateau orogeny to show that the mass flux across the lateral tips of this detachment controls the shape and kinematics of the plateau flanks if the mass flux is directed towards the plateau e g foreland crust moves into the detached section it forms a low slope small taper pro flank if the mass flux is directed outward thrusting towards the foreland generates a steep slope large taper retro flank the mass flux itself is controlled by the shear strength distribution at the base of the crust the two general types of orogenic flanks from three combinations that can be used to classify the evolution of plateau orogens in general application of this concept to the andes allows to decode the lower crustal shear strength distribution during the formation of the altiplano puna plateau their western slope is a retro flank localized by the underlying oceanic subduction zone on the eastern side a pro flank accretes foreland crust which is progressively decoupled from the moving mantle below

uplift of the western altiplano plateau evidence from the precordillera between 20 and 21 s northern chile 1 we present a quantitative reconstruction of uplift of the western flank of the altiplano plateau central andes one of the largest monoclines on the earth on the basis of an analysis of tectonic structures syntectonic deposits and geophysical data uplift occurred on a west vergent slowly propagating system of high angle reverse faults merging into a joint detachment that ramps down to midcrustal levels below the plateau edge the upper ramps determine local fold geometries while the lower ramp controls large scale surface tilting and uplift at 20 s this fault system was active between 30 ma and 5 10 ma with maximum shortening rates of 0 22 mm yr between 17 and 10 ma it generated some 2600 m of surface uplift with only minor shortening of 3000 m its activity was largely synchronous to eruption of large volume ignimbrites from a midcrustal source geophysical data indicate that the fault system localized deformation at the boundary between a cool strong forearc crust and a presumably fluid rich and or partially molten zone underneath the plateau area the systematic relation between crustal melting and shortening with uplift at the western plateau margin can be traced along most of the plateau flank with a stepwise decrease in age of deformation and magmatism toward the south indicating discontinuous addition of plateau segments crustal thickening to as much as 70 km from westward underthrusting in the back arc parts of the plateau isostatically compensated the tectonic surface uplift and monocline formation with respect to a stable forearc which only reacted with minor tilting

albedo of the south pole on mars determined by topographic forcing of atmosphere dynamics the nature of the martian south polar cap has remained enigmatic since the first spacecraft observations in particular the presence of a perennial carbon dioxide ice cap the formation of a vast area of black slab ice known as the cryptic region and the asymmetric springtime retreat of the cap have eluded explanation here we present observations and climate modelling that indicate the south pole of mars is characterized by two distinct regional climates that are the result of dynamical forcing by the largest southern impact basins argyre and hellas the style of surface frost deposition is controlled by these regional climates in the cold and stormy conditions that exist poleward of 60 degrees s and extend 180 degrees in longitude west from the mountains of mitchel approximately 30 degrees w surface frost accumulation is dominated by precipitation in the opposite hemisphere the polar atmosphere is relatively warm and clear and frost accumulation is dominated by direct vapour deposition it is the differences in these deposition styles that determine the cap albedo

a first look at dust lifting and dust storms near the south pole of mars with a mesoscale model surface wind stresses and dust lifting in the south polar region of mars are examined with a three dimensional numerical model the focus of this study is the middle to late southern spring period when cap edge dust lifting events are observed mesoscale model simulations of high southern latitudes are conducted at three dates within this season l s 225 255 and 310 assuming that dust injection is related to the saltation of sand sized grains or aggregates the mars mm5 mesoscale model predicts surface wind stresses of sufficient strength to initiate movement of sand sized particles 100 m and hence dust lifting during all three periods the availability of dust and or sand sized particles is not addressed within this study instead the degree to which the existence of sufficiently strong winds limit dust injection is examined by eliminating forcing elements from the model the important dynamical modes generating high wind stresses are isolated the direct cap edge thermal contrast and topographic slopes in some locations provides the primary drive for high surface wind stresses at the cap edge while sublimation flow is not found to be particularly important at these three dates simulations in which dust is injected into the lowest model layer when wind stresses exceed a threshold show similar patterns of atmospheric dust to those seen in recent observations comparison between these simulations and those without active dust injection shows no signs of consistent positive or negative feedback due to dust clouds on the surface wind stress fields during the late spring season examined here

mars atmospheric argon tracer for understanding martian atmospheric circulation and dynamics 1 one and one half mars years from 8 june 2002 to 2 april 2005 of atmospheric argon ar measurements are described and studied in the context of understanding how ar a minor constituent of the martian atmosphere that does not condense at temperatures found on mars can be used to study martian circulation and dynamics the ar data are from the gamma subsystem of the gamma ray spectrometer currently operating on the mars odyssey spacecraft in orbit around mars a comprehensive data analysis including ray production and attenuation by the atmosphere is presented four discoveries are discussed 1 there is a factor of 6 enhancement of ar measured over south polar latitudes 75 s to 90 s for 2 consecutive mars years occurring near the onset of southern winter 2 there is no similar strong enhancement of ar over north polar regions during northern winter part of this difference is explained by the global topographic dichotomy and the fact that the duration of northern autumn and winter is only 80 as long as that of southern autumn and winter 3 rapid seasonal fluctuations in ar abundance from 60 s to 90 s may be evidence for wave activity at the perimeter of the southern seasonal polar cap 4 the magnitude of the ar enhancement over the south polar region lacks spatial coincidence with either the relatively dark cryptic terrain or the relatively bright albedo regions however a divergence in ar abundance near ls 267 5 may be an expression of later co2 sublimation in the bright terrain rather than in the cryptic region

the spatial and seasonal distribution of martian clouds and some meteorological implications the spatial and seasonal distributions of martian atmospheric clouds organized according to simple morphologic criteria exhibit distinct patterns when interpreted self consistently using analogies to terrestrial cloud forms and martian temperature wind direction and water vapor measurements patterns of cloud occurrence provide some loose constraints on global scale near surface wind speed static stability and humidity we have examined all mariner 9 and viking orbiter images for this study we concentrate primarily on the larger viking data set whenever observations are possible relatively high near surface winds appear to follow the seasonal cap edges during early fall late winter and spring moderate to high winds are also inferred in mid latitudes for mid southern winter and in low latitudes mainly in the steeply sloping areas of tharsis near the solstices at other times lower winds are suspected hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule cloud occurrence data suggest that the near surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring relatively high static stability is deduced near the winter poles and globally during the dust storm season in spite of low atmospheric temperatures the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid latitudes during early winter during northern spring and summer saturation conditions seem to be easily achieved at mid latitudes and condensate clouds are abundant the situation is complicated by atmospheric dust in southern spring and summer low latitudes generally appear to be farther from saturation than mid latitudes and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons

the role of lithospheric heterogeneities in the location of the cenozoic intraplate deformation of iberia from finite element modeling received 31 may 2011 revised 28 november 2011 accepted 12 december 2011 published 9 february 2012 1 the cenozoic evolution of the central system basement uplift and of the continental duero and madrid basins on the iberian peninsula occurred in a compressive context triggered by the alpine orogeny although several models of deformation have been suggested the factors that led to the development of these have not been analyzed to date we present here finite element modeling of the intraplate deformation of the iberian lithosphere during the cenozoic this modeling has taken into account the role played by 1 the tectonic shortening originating from the pyrenean and betic collisions 2 the weight of tertiary continental sediments and 3 thermomechanical heterogeneities present in the lithosphere the numerical model represents a lithospheric section with a creep type mechanical behavior perpendicular to the central system and the two sedimentary basins both initial conditions and the results obtained have been specified based on the available geophysical and geological data this study has enabled us to simulate the present lithospheric structure of the central iberian peninsula a the formation of the central system relief and its horizontal shortening b the basement folding in the duero and madrid basins c the development of the root of the mountain range and d the depth of the lithosphere asthenosphere border in the interior of iberia the deformations occurred through a large scale folding and thickening mechanism by the shortening of a lithosphere that was initially thinner and with lateral contrasts in temperatures and composition

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

topography and subduction geometry in the central andes clues to the mechanics of a noncollisional orogen the central andean orogen between 12 and 32 s latitude exhibits a high degree of spatial order principally an extraordinary bilateral symmetry that is common to the earth s surface the underlying wadati benioff zone and the nazca south america plate kinematics which has been stable since the mid tertiary this spatial order must reflect the physical mechanisms of mountain building in this noncollisional orogen the shapes of the topography and subduction zone can be reduced to symmetric and antisymmeric components relative to any vertical symmetry plane the particular plane which minimizes the antisymmetry and maximizes the symmetry is well resolved and is essentially coincident with the stable euler equator of nazca south america relative motion since the mid tertiary that the topography subduction geometry and persistent mid tertiary plate kinematics share common spatial and geometric elements suggests that the distribution of topography in this orogen depends strongly on the dynamics of subduction other factors that might affect the topography and underlying tectonics such as climate and inherited structural fabric which have different spatial characteristics must be of less significance at a continental scale furthermore the small components of asymmetry among the various elements of the orogen appear to be mutually related in a simple way it is possible that this coupled asymmetry is associated with a late tertiary change in plate kinematics these observations suggest that there is a close connection between plate tectonics and the form of the earth s surface in this noncollisional setting it follows that the distribution of topography near convergent plate boundaries may provide a powerful constraint for understanding the dynamics of subduction

the evolution of deformation and topography of high elevated plateaus 2 application to the central andes the central andes form a wide elevated plateau flanked in the west by a steep slope toward the deep chilean trench and in the east by a gentle slope that subsides gradually toward the brazilian shield the low elevated trench topography is dynamically supported whereas the high andean mountain topography is mostly isostatically supported by a thick crust the last mountain building phase which thickened the crust and formed the present day andes began 26 m y ago in the late oligocene with the increase of the convergence rate between the nazca and the south american plates we investigate the time evolution of the andean deformation and topography by applying a temperature dependent viscoplastic flow model of continental lithosphere to the south american plate the model predicts the observed present day topographic profile across the central andes from the trench across the high altiplano plateau to the brazilian shield our numerical results combined with observations of the spatial and temporal distribution of igneous activity in the central andes lead us to conclude that the altiplano developed and extended to its present width of 400 km as a result of thermal weakening of the lithosphere since late oligocene until present the model also predicts the observed eastward migration of the locus of the andean crustal deformation with time at early stages both the crustal and mantle loci of deformation lie in the thermally weak region which results in crustal thickening in this finite region at later stages as the crust thickens it induces increased buoyancy forces which resist crustal thickening beyond 65 km as a result the locus of crustal deformation migrates eastward the detachment of the crustal locus of deformation from that of the mantle can explain the observed change in deformation pattern from thick skinned tectonism during early stages of the deformation to thin skinned tectonism during the more recent stages

evolution of the west andean escarpment at 18 s n chile during the last 25 ma uplift erosion and collapse through time abstract the geological record of the western andean escarpment warp reveals episodes of uplift erosion volcanism and sedimentation the lithological sequence at 18 s comprises a thick pile of azapa conglomerates 25 19 ma an overlying series of widespread rhyodacitic oxaya ignimbrites up to 900 m thick ca 19 ma which are in turn covered by a series of mafic andesite shield volcanoes between 19 and 12 ma the surface of the oxaya ignimbrites evolved into a large monocline on the western slope of the andes a giant antithetically rotated block oxaya block 80 km 20 km formed on this slope at about 10 12 ma and resulted in an easterly dip and a reversed drainage on the block s surface morphology topography and stratigraphic observations argue for a gravitational cause of this rotation a secondary gravitational collapse 50 km3 extending 25 km to the west occurred on the steep western front of the oxaya block alluvial and fluvial sediments 11 2 7 ma accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall indicating further shortening between 8 and 6 ma flatlying upper miocene sediments

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

erosion and tectonics at the margins of continental plateaus the topography across the eastern margin of the central andean plateau north of 18 s beni region bears a strong resemblance to the topography of the southern margin of the tibetan plateau nepal himalaya with both regions featuring a steep frontal slope and high peaks at the plateau edge in contrast the topography of the eastern margin of the central andean plateau south of 18 s pilcomayo region tapers toward the foreland more gently and has no line of high peaks at the margin both the himalayan and the beni regions have been the sites for large amounts of denudation and in both regions geologic evidence suggests that erosion has been sufficiently vigorous for the physiographic plateau margin to have retreated toward the plateau interior during the neogene we hypothesize that the steep frontal slope and high peaks of the beni region and himalayan front largely reflect the high orographic precipitation and high erosion rates occurring in these regions and that the more gentle topography of the semiarid pilcomayo region reflects a tectonic landform only slightly modified by erosion we propose that orographic precipitation impinging on a plateau margin will generally tend to drop moisture low on the slope eroding back the plateau while enhancing or maintaining the steep long wavelength slope a numerical model coupling orographic precipitation erosion and tectonic uplift demonstrates the plausibility of this hypothesis the erosional efflux in both the beni and nepal himalaya have been considerable and simple mass balance calculations for the himalaya suggest that during the neogene the erosional mass efflux has generally outpaced the tectonic mass influx this contrasts with the apparent prior domination of tectonic influx and may reflect a decrease in the rate of tectonic addition during the same period and or increased late cenozoic erosion rates

zonal wavenumber three traveling waves in the northern hemisphere of mars simulated with a general circulation model abstract observations suggest a strong correlation between curvilinear shaped traveling dust storms observed in wide angle camera images and eastward traveling zonal wave number m 3 waves observed in thermal data in the northern mid and high latitudes during the fall and winter using the marswrf general circulation model we have investigated the seasonality structure and dynamics of the simulated m 3 traveling waves and tested the hypothesis that traveling dust storms may enhance m 3 traveling waves under certain conditions our standard simulation using a prescribed mgs dust scenario can capture the observed major wave modes and strong near surface temperature variations before and after the northern winter solstice the same seasonal pattern is also shown by the simulated near surface meridional wind but not by the normalized surface pressure the simulated eastward traveling 1 4 t m 3 waves are confined near the surface in terms of the temperature perturbation ep flux and eddy available potential energy and they extend higher in terms of the eddy winds and eddy kinetic energy the signature of the simulated m 3 traveling waves is stronger in the near surface meridional wind than in the near surface temperature field compared with the standard simulation our test simulations show that the prescribed m 3 traveling dust blobs can enhance the simulated m 3 traveling waves during the pre and post solstice periods when traveling dust storms are frequently observed in images and that they have negligible effect during the northern winter solstice period when traveling dust storms are absent the enhancement is even greater in our simulation when dust is concentrated closer to the surface our simulations also suggest that dust within the 45 75 n band is most effective at enhancing the simulated m 3 traveling waves there are multiple factors influencing the strength of the simulated m 3 traveling waves among those our study suggests that weaker near surface static stability larger near surface baroclinic parameter and wave form dust forcing for latitudinally extended dust storms are favorable further study is needed to fully understand the importance of these factors and others

wave energetics of the southern hemisphere of mars abstract an assessment of the energetics of transient waves in the southern hemisphere of mars is presented using the mars analysis correction data assimilation macda dataset v1 0 and the eddy kinetic energy equation the dataset is divided into four representative periods covering the summer and winter solstices a late fall period and an early spring period for three mars years spring eddies are the most intense with eddies during the fall being less intense due to a marginally more stable mean temperature profile and reduced recirculation of ageostrophic geopotential fluxes compared to the spring eddy kinetic energy during winter is reduced in intensity as a result of the winter solstitial pause in wave activity and eddy kinetic energy during the summer is limited baroclinic energy conversion acts as a source in fall and spring but disappears during the winter as a result of a stabilized vertical temperature profile barotropic energy conversion acts as both a source and a sink of eddy kinetic energy being most positive during the solstitial pause eddies take a northwest to southeast track across the southern highlands in the fall but have a more zonal track in the spring due to stronger eddy kinetic energy advection wave energetics is less intense in the southern compared to the northern hemisphere as a result of a shallower baroclinically unstable vertical profile

consistency of geologic and geodetic displacements during andean orogenesis displacement and convergence rates inferred from gps and marine magnetic data suggest that this trend may be continuing at present hence an increasing fraction of convergence is being absorbed by mountain building this change may reflect increased plate coupling due to decreased sediment supply younger subducting lithosphere or increased normal stress at the interface from the effects of uplift index terms 8102 tectonophysics continental contract orogenic belts 8157 evolution of the earth plate motions past 3040 8158 evolution of the earth plate motions present and recent 3040 8099 structural geology general or miscellaneous

geochronology of pediment surfaces in southern peru implications for quaternary deformation of the andean forearc abstract the geomorphology of the andean forearc has historically been viewed as an old remnant of a late miocene planar landscape with no significant active structures accommodating quaternary deformation however the well preserved sequence of planation surfaces and strath terraces developed within the forearc of southern peru provide evidence of recent uplift along the western margin previously the abandonment of these surfaces was attributed to uplift of late miocene age however abrupt changes in topography and drainage incision within the pediment surfaces indicate recent deformation we use in situ produced 10be to determine the exposure ages of these abandoned surfaces in order to derive the spatial and temporal extent of this tectonic activity our new results in contrast to previous work yield pediment surface ages of 119 ka 203 ka 278 ka 549 ka and 1003 ka indicating a youthful morphology additionally these surfaces are affected by steeply dipping active faults producing localized deformation which can be quantified incision rates based on the exposure ages of abandoned strath surfaces are on the order of 0 04 0 3 mm yr the data set presented here not only suggests significant active deformation within the forearc but also highlights a sharp contrast between the style of deformation observed on the eastern and western margins of the andes while the general notion is that active deformation is localized in the subandean fold and thrust belt our data support an emerging view where active deformation is occurring in the western margin as well

curvilinear features in the southern hemisphere observed by mars global surveyor mars orbiter camera abstract we have used the complete set of mars global surveyor mgs mars daily global maps mdgms to study martian weather in the southern hemisphere focusing on curvilinear features including frontal events and streaks frontal events refer to visible events that are morphologically analogous to terrestrial baroclinic storms mdgms show that visible frontal events were mainly concentrated in the 210 300 e 60 150 w sector and the 0 60 e sector around the southern polar cap during l s 140 250 and l s 340 60 the non uniform spatial and temporal distributions of activity were also shown by mgs thermal emission spectrometer transient temperature variations near the surface streaks refer to long curvilinear features in the polar hood or over the polar cap they are an indicator of the shape of the polar vortex streaks in late winter usually show wavy segments between the 180 meridian and argyre model results suggest that the zonal wave number m 3 eastward traveling waves are important for their formation

marci and moc observations of the atmosphere and surface cap in the north polar region of mars abstract we used mgs moc and mro marci daily mapping images of the north polar region of mars from 16 august 2005 ls 270 to 21 may 2009 ls 270 covering portions of three consecutive martian years my 27 my 29 to observe the seasonal behavior of the polar ice cap and atmospheric phenomena the rate of cap regression was similar in my 28 and my 29 but was advanced by 3 5 of ls 7 8 sols in my 29 the spatial and temporal behaviors of dust and condensate clouds were similar in the two years and generally in accord with prior years dust storms 100 km2 were observed in all seasons with peak activity occurring at ls 10 20 from 50 n to 70 n and at ls 135 140 from 70 n to 90 n the most active quadrant was 0 90 w in my 28 shifting to 180 270 w in my 29 the majority of regional storms in both years developed in longitudes from 10 w to 60 w during late summer the larger storms obscure the north polar region in a cloud of dust that transitions to north polar hood condensate clouds around autumnal equinox changes in the distribution of perennial ice deposits especially in olympia planum were observed between the 2 years with the my 29 ice distribution being the most extensive observed to date modeling suggests that the small bright ice patches on the residual cap are not the result of slope or elevation effects rather we suggest that they are the result of local meteorological effects on ice deposition the annual darkening and brightening of peripheral areas of the residual cap around summer solstice can be explained by the sublimation of a brighter frost layer revealing an underlying darker ice rich layer that itself either sublimes to reveal brighter material below or acts as a cold trap attracting condensation of water vapor that brightens the surface an alternative explanation invokes transport and deposition of dust on the surface from the cap interior and later removal of that dust the decrease in cap albedo and accompanying increase in near surface atmospheric stability may be related to the annual minimum of polar storm activity near northern summer solstice

thermal tides and stationary waves on mars as revealed by mars global surveyor thermal emission spectrometer atmospheric temperature retrievals from thermal emission spectrometer tes observed radiances make possible the most complete separation of the constituent wave modes evident in mars atmosphere to date we use all of the data from the first aerobraking period as well as the science phasing orbits which affords good sampling of the diurnal tides and stationary waves tes retrievals of atmospheric temperature on a grid of pressure levels are the fundamental data set in this study we then fit this data to selected fourier modes in longitude and time for altitude latitude and ls bins from this we have identified the amplitudes and phases of the diurnal and semidiurnal tides the first few gravest stationary waves and a few modes which arise because of couplings between sun fixed tides and topography we also retrieve estimates of the zonal and time of day mean temperature meridional cross sections and their rates of change the zonal and time of day mean temperature meridional cross sections agree with those of conrath et al this issue to within 1 k where we can reliably retrieve this mode 90 s to 20 s heating rates of up to 2 4 k sol were observed around three scale heights above 60 s 90 s during the ls 310 320 dust storm diurnal tide amplitudes of greater than 8 k were observed during the noachis and ls 310 320 dust storms from ls 255 285 an unexplained phase reversal at two scale heights was observed in the diurnal tide from 60 s 80 s convective penetration above the unstable boundary layer may explain anomalous 180 out of phase with the sun diurnal tide phases between 0 5 and one scale height above the subsolar point semidiurnal tides are of order 2 k throughout the southern extratropics a stationary mode of wavenumber one was observed with amplitude 1 4 k in the southern extratropics topographically coupled tidal modes were also quantified

forced waves in the martian atmosphere from mgs tes nadir data abstract we have analyzed the temperature retrievals from mars global surveyor mgs thermal emission spectrometer tes nadir spectra to yield latitude height resolved maps of various atmospheric forced wave modes as a function of season for a full mars year among the isolated wave modes is the zonal mean time mean temperature which we used to derive zonal mean zonal winds and stationary wave quasi geostrophic indices of refraction diagnostic of their propagation the diurnal kelvin wave was isolated in the data with results roughly consistent with models wilson and hamilton 1996 j atmos sci 33 1290 1326 the s 1 and s 2 stationary waves were found to have significant amplitude in ducts extending up the winter polar jets while the s 3 stationary wave was found to be confined to near the surface the s 1 stationary wave was found to have little phase tilt with height during northern winter but significant westward phase tilt with height in the southern winter this indicates that the wave carries heat poleward slightly more than that found in barnes et al 1996 j geophys res 101 12 753 12 776 the s 1 stationary wave is likely the dominant mechanism for eddy meridional heat transport for the southern winter we noted that the phase of the s 2 stationary wave is nearly constant with time but that the s 1 stationary wave moved 90 of longitude from fall to winter and back in spring in the north while interannual variability is not yet addressed overall these results provide the first comprehensive benchmark for forced waves in mars s atmosphere against which future atmospheric models of mars can be compared

tectonic shortening and crustal thickness in the central andes how good is the correlation exceptional thickening of continental crust beneath the central andes is believed to be mainly a result of tectonic shortening of the south american plate in neogene time this shortening has been estimated to have contributed as much as 70 80 of the present crustal volume a compilation of published shortening values and our own estimates based on balanced cross sections from the central andes between lat 3 s and 40 s suggest that 70 80 is a maximum rather than an average value for this part of the andes tectonic shortening and the crustal cross section area are only loosely correlated variations in tectonic shortening are more abrupt than those of crustal areas particularly near the northern and southern ends of the altiplano puna high plateau where thick crust is associated with relatively small amounts of shortening shortening there may account for no more than about 30 of the present crustal cross section area the processes that created the remaining crustal area are not clear but are likely to involve poorly constrained pre neogene tectonic shortening moderate magmatic additions to the crust tectonic underplating of material derived from the forearc and possible flow of ductile lower crust along strike

fault associated salt flow and mass movement it has been suggested by model studies that swell formation may occur in a mobile layer subjected to faulting where the fault throw is less than the mobile layer thickness in such a case in the real earth differential overburden loading due to deposition or erosion at a later stage will cause a mobile layer e g salt rock to flow from the region of higher to the region of lower load stress via the fault zone resulting in swell formation on the upthrow side of the fault two different examples of this effect are illustrated in marine seismic sections from the north sea associated with one of these examples are seismic events which appear to indicate mass movement of sediment down the fault scarp prior to the deposition of the main body of zechstein halite at this location

andean growth and the deceleration of south american subduction time evolution of a coupled orogen subduction system article i nfo present day orography at the andean margin is a result of isostasy tectonic accretion and erosional processes the resulting excess mass of the andes gives rise to frictional stresses on the seismogenic plate interface that resist the sinking of the subducting slab into the upper mantle thus subduction rates should be sensitive to the time dependent dynamics of a back arc orogen as well as erosional or accretional processes that affect orogen growth here we develop a two dimensional coupled orogen slab model that allows for the prediction of orogen size and plate motion in response to both tectonic and erosional forcing we find that the frictional force exerted by the orogen on the subducting slab grows quadratically with orogen width and that the frictional resistance typically balances 10 50 of the slab pull force the time evolution of the coupled orogen subduction zone system is largely controlled by the rate of orogen growth which is controlled by the rate of convergence and the erosivity of the climate state in the case of the andean margin our models show that miocene aridification leads to reduced erosion increased orogen growth greater frictional resistance to subduction and ultimately to a 50 reduction in the convergence rate between the nazca and south american plates

moc observations of the 2001 mars planet encircling dust storm abstract from 15 september 1997 through 21 january 2006 only a single planet encircling martian dust storm was observed by mgs moc the onset of the storm occurred on 26 june 2001 l s 184 7 earliest recorded to date it was initiated in the southern mid to low latitudes by a series of local dust storm pulses that developed along the seasonal cap edge in malea and in hellas basin l s 176 2 184 4 the initial expansion of the storm though asymmetric was very rapid in all directions 3 32 m s 1 the main direction of propagation however was to the east with the storm becoming planet encircling in the southern hemisphere on l s 192 3 several distinct centers of active dust lifting were associated with the storm with the longest persisting for 86 sols syria claritas these regional storms helped generate and sustain a dust cloud haze which reached an altitude of about 60 km and a peak opacity of dust 5 0 by l s 197 0 the cloud had encircled the entire planet between 59 0 s and 60 0 n obscuring all but the largest volcanoes the decay phase began around l s 200 4 with atmospheric dust concentrations returning to nominal seasonal low levels at l s 304 0 exponential decay time constants ranged from 30 117 sols the storm caused substantial regional albedo changes darkening and brightening as a result of the redistribution removal and deposition of a thin veneer of surface dust at least 0 1 11 1 m thick it also caused changes in meteorological phenomena i e dust storms dust devils clouds recession of the polar caps and possibly surface temperatures that persisted for just a few weeks to more than a single mars year the redistribution of dust by large annual regional storms might help explain the long period 30 years between the largest planet encircling dust storms events

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

effect of the brittle ductile transition on the topography of compressive mountain belts on earth and venus the coulomb critical taper model has been very successful in explaining the large scale topography of a number of terrestrial accretionary wedges however this model is limited to cases of purely brittle frictional deformation in this paper we extend the range of applicability of the critical taper model by explicitly including the effects of temperature dependent ductile deformation the new model includes temperature dependent power law flow an assumed velocity field and linear thermal gradients in the atmosphere and within the crust flexural isostasy is also incorporated so that the decollement geometry is computed as a response to the applied load of the wedge material we assume that ductile deformation within the decollement zone is controlled primarily by diffusion flow whereas ductile deformation within the wedge itself is controlled by dislocation creep the topographic profiles predicted by the model are very similar to those of a number of fold and thrust belts on both earth and venus a typical wedge profile includes three distinctive topographic regions a narrow taper toe where both the wedge and the decollement zone deform in a brittle frictional manner a region of relatively steep slope where the wedge base deforms ductilely and the decollement zone is still frictional and a flat plateau region where both the wedge base and the decollement zone are deforming by ductile flow we have applied the model to two fold and thrust belts on venus maxwell montes and uorsar rupes and to the andes on earth and we find good agreement between observed and predicted topography using reasonable parameter values the model accounts for the observed positive correlation between relief and elevation of venusian fold and thrust belts on the basis of different thermal environments at different elevations it is also able to explain the first order differences between terrestrial and venusian fold and thrust belts fundamentally this difference is due to a combination of the lower temperatures and the presence of water on earth

north polar frontal clouds and dust storms on mars during spring and summer the complete archive of mars global surveyor mgs mars orbiter camera moc mars daily global maps mdgm are used to study north polar clouds and dust storms that exhibit frontal structures during the spring and summer ls 0 180 results show that frontal events generally follow the edge of the polar cap during spring and mid late summer with a gap in the distribution in early summer the exact duration and timing of the gap vary from year to year ten to twenty percent of spring and summer time frontal events exhibit complex morphologies distinct temperature signatures are associated with features observed in images in many but not all cases the general travel paths of the frontal events are eastward around the polar cap westward paths exist only at the edge of the polar cap in late spring early summer occasionally the paths curve toward or away from the polar cap in certain longitude sectors

martian clouds observed by mars global surveyor mars orbiter camera we have made daily global maps that cover both polar and equatorial regions of mars for ls 135 360 and 0 111 using the mars global surveyor mgs mars orbiter camera moc red and blue wide angle swaths taken from may 1999 to january 2001 we study the seasonal distribution of condensate clouds and dust clouds during roughly 1 martian year using these daily global maps we present the development and decay of the tropical cloud belt and the polar hoods the spatial and temporal distributions of lee waves and spiral clouds and an unusual aster cloud above the volcanoes consisting of rays around a central disk like the flower the tropical cloud belt contains mostly fibrous clouds during northern spring early summer and convective clouds during middle late northern summer the detailed development and decay of the tropical cloud belt is nonuniform in longitude two distinct stormy periods in late summer precede the formation of the north and south circumpolar hoods the north polar storms in late summer resemble baroclinic frontal systems on earth but contain both dust and condensate clouds spiral clouds occur only in the northern high latitudes and only during northern spring and summer the north polar hood displays a stationary wave number two structure during the fall and winter the south polar hood has fewer streak clouds and lee wave clouds than the north polar hood during this particular year the lee wave cloud abundance in the south had two peaks in early fall and late winter and the lee wave cloud abundance in the north had one peak in early fall

shocks in a box an analogue model of subduction earthquake cycles with application to seismotectonic forearc evolution 1 we introduce and test an experimental approach to simulate elastoplastic megathrust earthquake cycles using an analogue model and apply it to study the seismotectonic evolution of subduction zones the quasi two dimensional analogue model features rate and state dependent elastic frictional plastic and viscoelastic material properties and is scaled for gravity inertia elasticity friction and viscosity the experiments are monitored with a high resolution strain analysis tool based on digital image correlation particle imaging velocimetry piv providing deformation time series comparable to seismologic geodetic and geologic observations in order to separate elastic and nonelastic effects inherent the experimental deformation patterns we integrate elastic dislocation modeling edm into a hybrid approach we use the analogue earthquake slip and interseismic locking distribution as edm dislocation input and forward model the coseismic and interseismic elastic response the residual which remains when the edm prediction is subtracted from the experimental deformation pattern highlights the accumulation of permanent deformation in the model the setup generates analogue earthquake sequences with realistic source mechanisms and elastic forearc response and recurrence patterns and reproduces principal earthquake scaling relations by applying the model to an accretionary type plate margin we demonstrate how strain localization at the rupture peripheries may lead to a seismotectonically segmented forearc including a tectonically stable shelf and coastal high 20 plate convergence accommodated by internal shortening overlying the area of large megathrust earthquake slip fifty to 75 of plate convergence is accommodated by internal shortening in the slope region where earthquake slip tapers out toward the trench the inner forearc region remains undeformed and represents a basin

the origin evolution and trajectory of large dust storms on mars during mars years 24 30 1999 2011 abstract mars daily global maps mdgm derived from the mars global surveyor mgs mars orbiter camera moc and mars reconnaissance orbiter mro mars color imager marci are used to study the distribution and evolution of large dust storms over the period from mars years 24 30 1999 2001 large storms are defined here as discrete dust events visible in image sequences extending over at least 5 sols mars days and where the dust covers areas beyond the origination region a total of 65 large dust storms meeting these criteria are identified during the observational period and all are observed during the l s 135 30 seasonal window dust storms originating in the northern and southern hemispheres appear to form two distinct families all but two of the storms originating in the northern hemisphere are observed in two seasonal windows at l s 180 240 and l s 305 350 while all but two of those originating in the southern hemisphere are observed during l s 135 245 none of the large dust storms originating in the northern hemisphere are observed to develop to global scale but some of them develop into large regional storms with peak area 1 10 7 km 2 and duration on the order of several weeks in comparison large dust storms originating in the southern hemisphere are typically much smaller except notably in the two cases that expanded to global scale the 2001 and 2007 global storms distinct locations of preferred storm origination emerge from the dust storm image sequences including acidalia utopia arcadia and hellas a route trajectory graph for the observed sequences is provided the routes are highly asymmetric between the two hemispheres in the south for non global dust storms the main routes are primarily oriented eastwest whereas in the north the routes are primarily north south and zonally concentrated into meridional channels in a few impressive cases storms originating in the northern hemisphere are observed to flush through acidalia and utopia across the equator and then branch in the low and mid southern latitudes the origin of the 2007 global dust storm is ambiguous from the imaging data immediately prior to the global storm a dust storm sequence from chryse is identified this storm s connection to the explosive expansion observed to start from noachis west hellas is unclear due to image coverage this paper further identifies and describes three different styles of dust storm development which we refer to as consecutive dust storms sequential activation and merging the evolution of a given dust storm sequence can exhibit different combinations of these growth styles at different stages of development dust storm sequences can overlap in time which makes them good candidate to grow into larger scale

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

origin of the high plateau in the central andes bolivia south america the bolivian altiplano in the central andes of south america is part of the second largest high plateau on earth it is an elongate region of subdued relief 1 2 105 km2 and 4 km above sea level bounded by the eastern cordillera and volcanic arc western cordillera here the crust is up to 75 km thick we describe the cenozoic geological evolution of this region using a revised chronostratigraphy and an analysis of the crustal and lithospheric structure crustal shortening and magmatic addition and locally sedimentation are the main mechanisms of cenozoic crustal thickening leading to nearly 4 km of surface uplift since the paleocene addition of mafic melts appears to be a first order mechanism of cenozoic crustal growth contributing 40 of the crustal thickening beneath the volcanic arc removal of the basal part of the lithosphere may have caused two episodes of widespread arc and behind arc mafic volcanism at 23 ma and 0 5 ma contributing to the surface uplift the altiplano originated as a sedimentary basin several hundred kilometers wide between the proto western cordillera and a narrow zone of uplift proto eastern cordillera farther east the latter zone formed by inversion of the center of a wide lacustrine or marine cretaceous paleocene basin close to sea level at 45 ma a thickness of 2 4 km of paleogene continental elastics accumulated in the proto altiplano basin subsequently in the oligocene we estimate that this region and the western margin of the eastern cordillera were technically shortened 22 65 km resulting in 9 km of average crustal thickening the altiplano basin was rejuvenated at 25 ma and subsequently flooded with up to 8 km thickness of detritus eroded from the uplifting eastern and western cordilleras between 25 and 5 ma folding and thrusting in the western margin of the eastern cordillera migrated westward into the center of the altiplano basin essentially terminating deposition except in local subbasins and accommodating 13 30 km of shortening and an estimated 7 km of average crustal thickening subsequently there has been strike slip deformation and limited local thrusting 5 km of shortening geomorphological and geochronological evidence for 1 5 2 km of surface uplift of this region since the late miocene suggests 14 km of lower crustal thickening beneath an essentially rigid lid and can be explained by 100 150 km of underthrusting of the brazilian shield and adjacent regions beneath the eastern margin of the central andes the present subdued relief in the altiplano may be a result of ductile flow in the lower crust and sedimentation and erosion in an internal drainage basin

observations of the initiation and evolution of the 2001 mars global dust storm 1 a global dust storm occurred on mars between june and october 2001 the storm began near hellas just before southern spring equinox ls 177 local storms likely forced by a combination of slope flow and ice cap thermal contrasts were observed to propagate along the northwestern rim of hellas apparently triggering the global storm cap edge storm activity for much of late southern winter was similar in 2001 to one mars year earlier however a very large storm propagated into the basin just after ls 177 subsequently the total area of storm activity in 2001 was roughly double that of the previous year for about 10 days dust lifting was limited to the hellas region as additional storms propagated into hellas activity built and extended northward into syrtis and eastward into hesperia it is not clear whether transport or spreading of lifting were of greatest importance for expansion at ls 185 the storm began to spread rapidly to the east along a line from the southern pole to the northern tropics essentially no storm propagation to the west occurred yielding strong zonal asymmetry of expansion as the dust storm reached the western edge of tharsis secondary dust lifting centers developed in daedalia and solis southeastern tharsis subsequently the storm rapidly encompassed the planet by ls 193 once fully global the syria solis daedalia lifting center appeared to dominate on the basis of cloud top morphology with hellas quiescent by ls 212 lifting could no longer be discerned thereafter dust haze appeared uniform and diffuse and decay appeared to have set in

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

traveling waves in the martian atmosphere from mgs tes nadir data abstract we have characterized the annual behavior of martian atmospheric traveling waves in the mgs tes data set from the first two martian years of mapping there is a high degree of repeatability between the two years they are dominated by strong low zonal wavenumber waves with high amplitudes near the polar jets strongest in late northern fall and early northern winter the m 1 waves have amplitudes up to about 20 k are vertically extended and occasionally extend even into the tropics periods for m 1 range from 2 5 to 30 sols much weaker waves were identified in the south with amplitudes less than about 3 5 k traveling waves with m 2 and m 3 are also seen but their amplitudes are typically limited to less than 4 k and are generally more confined near the surface in the north they are more evident in fall and spring rather than winter solstice which is clearly dominated by m 1 waves some evidence of storm tracks has been identified in the data with accentuated weather related temperature perturbations near longitudes 200 to 320 e for both the southern and northern hemispheres near latitude 65 at the surface some evidence was also found for a sharpening of longitudinal gradients into what may be frontal systems ep flux divergences show the waves extracting energy from the zonal mean winds when the m 1 waves were strongest decelerations of the zonal jet of order 30 m s sol were measured above 1 scale height the waves extract energy from the jet predominately through barotropic processes but their character is overall mixed barotropic baroclinic inertial instabilities may exist at altitude on the equatorward flanks of the polar jets and marginal stability extends through to the tropics this may explain the coordination of the tropical behavior of the waves with that centered along the polar jet consistent with the ideas expressed in wilson et al 2002 geophys res lett 29 1684 and similar to those in barnes et al 1993 j geophys res 98 3125 3148 throughout the year there exist large regions with the meridional gradient of pv less than zero but they are strongest near winter solstice poleward of the winter jet the regions of instability reach the surface equatorward they do not these regions satisfying a necessary criterion for instability likely explain the genesis of the waves and perhaps also their bimodal character between surface faster waves and altitude slow m 1 waves

how does trench coupling lead to mountain building in the subandes a viscoelastoplastic finite element model 1 subduction induced crustal shortening is believed to be the primary cause of the andean mountain building the present day crustal shortening in the andes is clear from the gps measurements but the rate 30 40 mm a is higher than the geological shortening rate 15 mm a suggesting that much of the present day crustal shortening may recover during future earthquakes in the subduction zone using a two dimensional viscoelastoplastic finite element model we investigate here how the cyclic trench coupling leads to long term mountain building which has been concentrated in the subandes in the past few million years our results show that much of the gps measured crustal shortening in the andes can be explained by the interseismic and postseismic viscoelastic strain that does not contribute to mountain building the apparently discordant gps and geological data can be reconciled in the geodynamic model with a weakened crust in the subandes which allows accumulation of plastic strains that leads to mountain building the localized crustal weakening and mountain building in the subandes may have been a consequence of the uplifted high andes the accelerated westward drift of the south american plate the possible delamination of mantle lithosphere under the eastern cordillera and the increasing trench coupling

end member models for andean plateau uplift abstract diverse techniques have been applied over the past decade to quantify the uplift history of the central andean plateau ap in this study opposing models for surface uplift are evaluated including a rapid rise of 2 5 km 10 6 ma and a slow and steady rise since 40 ma these end member models are evaluated by synthesizing observations of the ap lithosphere and the history of deformation sedimentation exhumation magmatism uplift and fluvial incision structural and geophysical studies estimate variable shortening magnitudes 530 150 km involving cover to basement rocks an isostatically compensated thick crust 80 65 km high heat flow and zones of variable velocity and attenuation in the crust and mantle these observations have invoked interpretations such as a hot weak lithosphere partial melt crustal flow and perhaps current localized delamination but do not provide strong support for massive delamination required by the rapid uplift model deformation and associated exhumation began 60 40 ma and generally migrated eastward with consistent long term average shortening rates 12 8 mm yr in bolivia favoring the slow uplift model volcanic and helium isotope evidence show an ap wide zone of shallow mantle melting and thin lithosphere that has existed since 25 ma which is inconsistent with the rapid rise model that suggests lithospheric thinning occurred 10 6 ma paleoaltimetry data suggest a rapid 2 5 km elevation gain 10 to 6 ma but are equally consistent within error with a linear rise since 25 ma widespread fluvial incision 2 5 1 km occurred along the western flank since 11 8 ma and may be associated with surface uplift as proposed by the rapid rise model however the paleoaltimetry and incision data can also be explained by regional climate change associated with plateau uplift implications of these results for reconstructions of ap evolution are that 1 substantial deformation of a weak lithosphere is essential 2 ap growth has taken significantly longer 40 myr and was more uniform along strike 1500 km than previously appreciated and 3 the slow and steady uplift model is most consistent with available constraints we conclude that the rapid uplift model may be an overestimate and that a more protracted cenozoic uplift history is tenable

magmatic arc tectonics in the central andes between 21 and 25 s abstract in northern chile four magmatic arc systems each displaced towards the east in relation to the previous one developed in sequence since the lias this migration of the magmatic arc from the coastal cordillera to the western cordillera probably was a consequence of tectonic erosion of the continental margin within each of these systems tectonic deformation took place contemporaneously to magmatic activity as the continental crust of the upper plate has been weakened in the area of the magmatic arc by the igneous processes it is relatively sensitive to the stresses introduced by plate convergence a very important factor for the deformation in the magmatic arc is the angle of convergence obliqueness which may cause shortening if obliqueness is small

transition from basement involved to thin skinned thrusting in the cordillera oriental of southern bolivia the eastern flank of the central andes in southern bolivia and northern argentina is underlain by a fold and thrust belt of neogene age it comprises an external thin skinned segment with basal detachment in silurian shales subandean ranges and an internal segment where units as deep as precambrian metasedimentary and igneous rocks are involved in thrusting eastern cordillera oriental between the cordillera oriental and the subandean ranges an intermediate segment interandean zone intervenes north of the argentinian bolivian border 22 s the structure of the interandean zone is characterized by folded and thrust faulted cambrian to triassic strata balanced cross sections across the western subandean ranges the interandean zone and the eastern cordillera oriental are based on previously available data and recent field work they suggest that the geological structure can be interpreted in terms of two major basement involved thrusts here referred to as interandean and subandean thrusts the more internal interandean thrust caused the development of broad basement anticlines in the eastern cordillera oriental however at shallower levels its displacement was accommodated by thin skinned folding and thrusting in the interandean zone in sequence activation of the subandean thrust uplifted the interandean zone on top of an imbricate basement sheet and caused the development of the thinskinned subandean ranges farther east published radiometric data and subsidence history of the subandean foreland basin suggest that the interandean thrust was active between about 10 ma and 5 ma the subandean thrust is still active southward displacement transfer from the subandean thrust onto the interandean thrust and a southward dipping lateral ramp of the interandean thrust result in the gradual transition from the interandean zone north of 22 s to the cordillera oriental of northern argentina a similar but larger scale transfer may be involved in the southern termination of the thin skinned subandean ranges of argentina at 23 s shortening in the western part of the thrust belt is of the order of 80 90 km total shortening in the eastern andean thrust belt from the undeformed foreland to the eastern margin of the cordillera oriental is 140 150 km

influence of basement faults on the development of salt structures in the danish basin scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the danish basin the models consisted of a viscous layer simulating rock salt overlain by layers of cohesive sand that mimic brittle failure in natural overburdens model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the danish basin in plan view model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement with further burial single diapirs rose from these buoyant walls some of the diapirs surfaced through the faulted overburden a few were trapped beneath the competent cretaceous units and others were starved due to lack of supply from below in section model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south where they rise diapirically in the model the pressure due to loading by overburden layers changed from 1 3 102 pa in the south to 2 3 102 pa in the northern part of the basin in general the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half grabens and introducing a slope and steps at the base of the buoyant layer weakening its overburden and causing differential loading and compaction the spreading overhangs of salt diapirs beneath the cretaceous chalk in the danish basin would seal any potential pre cretaceous reservoir rocks

the role of climate during high plateau formation insights from numerical experiments abstract high plateaus are elevated areas of low relief mostly associated with compressional tectonics and characterized by dry climatic conditions results from a novel computer modeling technique integrating surface and tectonic processes suggest that a pre existing dry climate through its effects on surface transport and orogenic evolution can significantly contribute to the formation of high plateaus according to these results dry climatic conditions promote sediment trapping within the orogen transferring the accommodation of tectonic shortening towards the external parts of the orogen and leading to the formation of a high plateau this feedback operates in the following steps 1 dry climatic conditions at the early stages of orogenesis favor the tectonic defeat of rivers draining the orogen promoting internal drainage endorheism 2 endorheism extends the life of intramountain basins maximizing the mass trapped within the orogen and expelling deformation further into the foreland and 3 this propagation of deformation further isolates the central parts of the orogen from incoming precipitation reinforcing sediment trapping and topographic leveling of the intramountain region this phenomenon allows reproduction of basic topographic drainage and tectonic differences between orogens lacking a high plateau such as the alps and orogens with a well developed high plateau like the andes without invoking inherited heterogeneities in the crust or other tectonic processes it also suggests that internal drainage and high plateaus might be a natural stage of orogenesis undergoing dry climatic conditions in the light of recent data reporting dry climate prior to the formation of the andean high plateau aridity can be seen as one of the causes for the formation of the altiplano rather than just as a consequence of topographic growth

the shaping of salt diapirs abstract six parameters shape the geometry of passive diapirs associated with stiff overburden rates of salt supply s dissolution d sediment accumulation a erosion er extension e and shortening sh these parameters change in space and time and hence influence the geometry of the structure as it forms a complex six parameter plot representing the evolution history of a salt diapir can be simplified into three separate graphs this study recommends adding to plots of s against a a second of rate of salt supply s this time with extension rate e and a third of rate of sediment accumulation a plotted against extension rate e integrating these three plots on a single diagram results in a complete description of the evolution history of a diapir when it is applied to three dimensional data however if applied to a profile the plot shows only the two dimensional evolution history of the diapir lateral forces extension or compression have a significant role in moulding the geometry of a salt diapir by influencing the space which it occupies by incorporating extension in the moulding plots of salt diapirs this study introduces the rate of sediment accumulation multiplied by extension e a as a significant factor in moulding salt diapirs by using this rate against the rate of salt supply this study redefines the conventionally accepted interpretation of upward narrowing upward widening and columnar diapirs upward narrowing diapirs form when the rate of salt supply is less than the rate of sediment accumulation multiplied by extension upward widening diapirs form when the salt supply is greater than the rate of sediment accumulation multiplied by extension columnar diapirs form when the rate of salt supply is equal to the rate of sediment accumulation multiplied by extension this new relationship explains the absence of columnar and upward widening diapirs in passive margins where thin skinned extension dominates and emphasizes the significance of lateral movement extension and shortening in moulding the geometry of salt diapirs

pure and simple shear plateau uplift altiplano puna argentina and bolivia abstract the concepts of pure and simple shear strain provide a meaningful way of discussing the alternative modes of lithospheric shortening which produced uplift of the central andean plateau since 10 ma discrete segments of the plateau exemplify pure or simple shear modes characteristics of the simple shear mode are a flanking thin skinned thrust belt and subdued relief and lack of significant late miocene to recent deformation within the plateau the pure shear mode is characterized by more rugged internal relief and active neotectonic deformation within the plateau and thick skinned foreland deformation involving seismic deformation of the crust to 30 km or more these modes of crustal thickening correlate with changes in lithosphere thickness modes of isostatic compensation broad wavelength topography and back arc magmatism the correlation of the boundary between pure and simple shear segments with major changes in pre existing anisotropies in the foreland of the orogen suggests that events which long pre date the andean orogeny indirectly controlled the along strike variation in the magnitude and style of shortening in the central andes and may have influenced the development of flat subduction

out of plane motion of a thrust sheet during along strike propagation of a thrust ramp a distinct element approach abstract using a 3d distinct element mechanical modeling program we examined the nature and magnitude of out of plane motion during along strike propagation of a simple thrust ramp and attendant fault related folding our numerical model was composed of about 83 000 spherical elastic particles that were bonded together to create an initial solid numerical rock mass capable of macroscopic fracture and faulting in response to displacement loading the algorithim is fully dynamic and as such allowed for the storage and sudden release of elastic strain energy in the form of seismic events we induced progressive along strike fault growth and attendant non cylindrical fold development by varying the along strike friction within a seeded planar zone of weakness within the aggregate a zone that was to become the fault the result was a well developed plunging ramp anticline that grew in amplitude and along strike length as the macroscopic fault propagated from lower to higher friction regions lateral fault propagation was relatively rapid compared with shortening with a ratio of thrust displacement to propagation length k of 6 5 incremental motion of the particles reflected episodic slip at both the laterally propagating fault tip and along the existing fault these episodes were characterized by local clusters of outward radiating velocity vectors that propagated at seismic velocities marking the model equivalents of earthquakes the finite displacement vectors in the hanging wall were approximately parallel to the far field transport direction with a strike parallel component that ranged from one to two orders of magnitude less than the strike perpendicular component furthermore about two thirds of the particles had strike parallel motion in the direction of fault propagation and fold plunge because the far field shortening boundary conditions were uniformly perpendicular to fault strike this component of motion in the plunge direction was apparently due to a topographically induced plunge parallel shear stress the along strike motion involved slip on the main fault as well as transient strike slip on minor vertical sometimes conjugate zones apparently induced by the increased topographic load

transient eddies in the southern hemisphere of mars 1 mars global surveyor is providing the first observations of transient eddies in the southern hemisphere of mars we derive basic properties of the traveling eddies that appear in midwinter ls 134 148 through analysis of radio occultation measurements at 67 70 s latitude the dominant mode has a period of 2 solar days and a zonal wavenumber s 3 strong zonal variations in eddy amplitude signal the presence of a possible storm zone at 150 330 e longitude within this longitude band the eddies achieve peak amplitudes at the 300 pa pressure level of 7 k in temperature and 10 15 m s 1 in meridional wind speed the minimum temperature associated with the eddies is 2 k colder than saturation of co2 close to the threshold where nucleation and growth of new ice particles can occur a simulation by a mars general circulation model produces traveling eddies that closely resemble the observations

cloud tracked winds for the first mars global surveyor mapping year we have measured winds using cloud motion in consecutive mars global surveyor mgs mars orbiter camera moc wide angle global map swaths taken during the first mapping year l s 135 360 111 we present a total of 11 200 wind vectors collected in the north polar region during l s 135 195 late summer early fall and l s 20 55 mid spring and in the south polar region during l s 337 10 late summer early fall for cases with good coverage we also present the derived mean zonal and meridional winds and the associated eddies the speed of the zonal winds in 60 n 70 n increases at 0 6 m s l s in late northern summer and that in 60 s 70 s increases at a rate of 0 7 m s l s in late southern summer the latitudinal distribution of zonal wind within 50 n 75 n from mid northern summer to early northern fall indicates that winds at higher latitudes are generally weaker than those at lower latitudes but the rate of increase with time is faster at higher latitudes there is a cyclonic gyre in the 90 w 0 30 e sector in the north polar region there are large scale waves in the weekly mean meridional wind and in the biweekly mean eddy momentum flux and eddy kinetic energy fields in the north polar region from mid to late summer the cloud tracked winds in the north are generally consistent with winds calculated by general circulation model at the water condensation level derived from mgs thermal emission spectrometer tes observations but appear stronger than the gradient winds derived from tes assuming no flow at the surface

diurnal variation and radiative influence of martian water ice clouds 1 we have identified regions in the martian tropics with anomalously warm nighttime surface temperatures the seasonal evolution of these anomalies is strongly correlated with the waxing and waning of the tropical cloud belt that is most prominent during northern hemisphere summer we attribute the anomalies to enhanced downward infrared radiation from water ice clouds the close agreement with spatial maps of atmospheric extinction derived from mars orbiter laser altimeter radiometry strongly supports this interpretation we show that a mars general circulation model simulation with radiatively active water ice clouds is able to reasonably match the observed spatial pattern and amplitude of the surface temperature anomaly the nighttime clouds are most prominent in the tharsis and arabia regions and are thicker optical depth 1 and more extensive than daytime clouds our cloud retrievals are the first to spatially map the nighttime clouds and provide an estimate of their thermal influence

major dust storms and westward traveling waves on mars westward traveling waves are observed during major dust storm periods in northern fall and winter the close correlation in timing makes westward traveling wave one of the signature responses of the martian atmosphere to major dust storms westward traveling waves are dominated by zonal wavenumber m 1 in the middle atmosphere and are typically characterized by long wave period they are associated with significant temperature perturbations near the edge of the north polar vortex their wind signals extend to the low latitudes and the southern hemisphere their eddy momentum and heat fluxes exhibit complex patterns on a global scale in the middle atmosphere

subduction of asian lithospheric mantle beneath tibet inferred from models of continental collision the relative northward motion of the indian subcontinent that followed the onset of continental collision with asia has produced extensive deformation of the earth s crust giving rise to the world s highest mountains in the himalayan chain and the world s largest high elevation region the tibetan plateau the formation of the broad mountain belt implies that contrary to the original tenets of plate tectonics the lithospheric plates have experienced widespread deformation far from the plate boundary1 several models have been proposed2 6 to explain the manner in which this post collisional deformation is distributed within the continental lithosphere of the indian and asian plates here we propose an alternative model in which subduction of the asian lithospheric mantle develops following the collision of india our model is supported by numerical calculations of crustal deformation and thickening and is consistent with available geological and geophysical data7 9 this picture suggests that lithospheric mantle is not deformed along with the crust and would imply that continental collision zones are more analogous to oceanic subduction zones than was previously believed

global patterns in cloud forms on mars abstract mariner 9 images and all viking orbiter images through july 1979 were searched for cloud forms a computer accessible catalog was assembled consisting of a classification of cloud type lee wav wave for example and properties directionality wavelength for example lee wave directionality shows a pattern and seasonal variation at high latitudes which is consistent with predictions of theoretical modeling fog and haze occurrence shows no obvious correlation with water abundance or any other simple causal factor lee waves are rare at equatorial latitudes plumes probably dust occur preferentially at locations where strong boundary layer convection is expected

further observations of regional dust storms and baroclinic eddies in the northern hemisphere of mars abstract we have investigated the near surface meteorology in the northern hemisphere of mars through detailed analysis of data obtained with mars global surveyor in january august 2005 the season in the northern hemisphere ranged from midsummer through winter solstice of mars year my 27 we examined composite wide angle images from the mars orbiter camera and compiled a catalog of the dust storms that occurred in this interval as in previous martian years activity in the northern hemisphere was dominated by regional flushing dust storms that sweep southward through the major topographic basins most frequently in acidalia planitia we also used atmospheric profiles retrieved from radio occultation experiments to characterize eddy activity near the surface at high northern latitudes there are strong correlations between the two sets of observations which allowed us to identify three factors that influence the timing and location of the regional dust storms 1 transitions among baroclinic wave modes which strongly modulate the intensity of meridional winds near the surface 2 storms zones which impose strong zonal variations on the amplitude of some baroclinic eddies and 3 stationary waves which further modulate the wind field near the surface the flushing dust storms ceased abruptly in midautumn possibly in response to source depletion co 2 condensation a shift in the period of the baroclinic eddies and changes in the tidal wind field near the surface our results extend the meteorological record of the northern hemisphere substantiate the findings of previous investigations and further illuminate the climatic impact of baroclinic eddies