stability and localization of rapid shear in fluid saturated fault gouge 2 localized zone width and strength evolution field and laboratory observations indicate that at seismic slip rates most shearing is confined to a very narrow zone just a few tens to hundreds of microns wide and sometimes as small as a few microns rice et al 2014 analyzed the stability of uniform shear in a fluid saturated gouge material they considered two distinct mechanisms to limit localization to a finite thickness zone rate strengthening friction and dilatancy in this paper we use numerical simulations to extend beyond the linearized perturbation context in rice et al 2014 and study the behavior after the loss of stability neglecting dilatancy we find that straining localizes to a width that is almost independent of the gouge layer width suggesting that the localized zone width is set by the physical properties of the gouge material choosing parameters thought to be representative of a crustal depth of 7 km this predicts that deformation should be confined to a zone between 4 and 44 m wide next considering dilatancy alone we again find a localized zone thickness that is independent of gouge layer thickness for dilatancy alone we predict localized zone thicknesses between 1 and 2 m wide for a depth of 7 km finally we study the impact of localization on the shear strength and temperature evolution of the gouge material strain rate localization focuses frictional heating into a narrower zone leading to a much faster temperature rise than that predicted when localization is not accounted for since the dynamic weakening mechanism considered here is thermally driven this leads to accelerated dynamic weakening

dark slope streaks on mars are aqueous processes involved 1 concentrations of dark slope streaks occur in the equatorial latitudes of mars mostly where magmatic driven activity dominates the geologic record although originally ascribed to wet debris flows all the most recent published hypotheses concerning these features focus on processes which disturb a brighter dusty mantle to expose a darker substrate these mechanisms invoke dry mass wasting or eolian processes excluding a role for water in light of the geographic geologic and morphologic considerations and the new information provided from the mars orbital camera and the mars orbital data altimeter we reexamine fluvial processes as a viable explanation for some of the dark slope streaks in our opinion two contrasting processes for the formation of dark slope streaks dust avalanching and spring discharge represent endpoints on a continuum of progenitors it may be that some of these features result from dry mass wasting or eolian processes some from fluvial processes and some from a mechanism s not yet conceived a spring discharge origin for the formation of the dark slope streaks has profound implications including mars having limited but currently active fluvial processes acting upon its surface as well as near surface aquifers

seasonal formation rates of martian slope streaks abstract slope streaks are gravity driven dark or light toned features that form throughout the martian year in high albedo and low thermal inertia equatorial regions on mars these distinctive features have never been observed in a terrestrial environment although some analogs have been proposed based on diverse orbital observations a number of mechanisms including granular and aqueous flows have been proposed to explain their formation using multi temporal images taken by the context camera ctx aboard the mars reconnaissance orbiter mro we identified newly formed streaks in multiple martian years and estimated seasonal streak formation rates at intermediate latitudes as well as at the equator we found seasonal variations in streak activity in multiple consecutive martian years including high formation rates during autumn solar longitude ls 190 during this time slope streak activity exceeds the long term formation rate multiple times the highest seasonal formation rate of 0 16 per streak per martian day was observed in the olympus mons aureole in autumn ls 210 of mars year 30 in some sites slope streak formation rate at slopes of opposite orientation peaks at different seasons the seasonal variations of the formation rate are inconsistent with sporadic trigger mechanisms and revealed that changing conditions at the slopes affect the formation of the streaks throughout the martian year modelled environmental parameters at the streak bearing slopes indicate a correlation between seasonal streak activity and surface temperature as well as wind velocity seasonal variations of streak activity could be a result of varying intensities of both dry and wet mechanisms or could be explained by the interaction of multiple mechanisms

fluid dynamical implications of anastomosing slope streaks on mars 1 the mars global surveyor mission has imaged slope streaks some of which have formed in periods as short as 109 days these features are one of the most currently active surface processes on mars some slope streaks have flow like morphologic characteristics which include anastomosing patterns influenced by small topographic barriers in order to understand what processes gave rise to these specific features we applied viscoplastic flow numerical modeling techniques to simulated martian surfaces we simulate martian surfaces with observed slope streaks by using mars orbiter laser altimeter measurements to obtain large scale slope measurements and a photoclinometry technique on mars orbiter camera images to obtain meter scale topographic information our numerical simulations of slow moving plastic flows show that a fluid rheology and a short formation period are necessary to explain these features we estimate that the typical values of bulk viscosity and bulk yield strength are less than 10 pa s and less than 10 pa respectively the fluid rheology can be explained by a water related flow with a solid content less than about 20 an alternative explanation is a dry grain flow with extremely low cohesion and friction angle supported by dispersive pressure or a lubricant such as electric conditions of particles the continuous nature of anastomosing slope streaks that originate from point sources is best explained by continuous discharges of material or lubricant in this case the estimated flow rate is less than several cubic meters per second and the flow duration is estimated to be less than a day

the structure of an exhumed intraplate seismogenic fault in crystalline basement abstract the 600 m thick gole larghe fault zone glfz is hosted in jointed crystalline basement and exposed across glacier polished outcrops in the italian alps ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes solidified frictional melts formed at 9 11 km depth and ambient temperatures of 250 300 c previous work focused on the southern part of the fault zone here we quantitatively document fault zone structure across the full width of the glfz and surrounding tonalite host rocks by using a combination of structural line transects and image analysis of samples collected across fault strike these new datasets indicate that the glfz has a broadly symmetric across strike damage structure and contains distinct southern central and northern zones distinguished by large variations in fracture density distribution of pseudotachylytes volume of fault rock materials and microfracture sealing characteristics the c 100 m wide central zone is bound by two thick 2 m and laterally continuous 1 km protocataclastic to ultracataclastic horizons within and immediately surrounding the central zone fracture density is relatively high due to cataclastic fault fracture networks that reworked earlier formed pseudotachylytes the fault fracture networks were associated with pervasive microcracking and fluid rock interaction resulting in the development of a c 200 m thick alteration zone delimited by lobate fluid infiltration fronts in the c 250 m thick southern and northern zones fracture densities are much lower and pseudotachylytes systematically overprint cataclastic faults that exploited pre existing magmatic cooling joints analysis of the structure of the glfz suggests that it shares certain characteristics with the seismogenic source responsible for the 2002 au sable forks intraplate earthquake sequence in the northeastern usa including seismicity distributed across a fault zone 500 1000 m thick and large 100 mpa static stress drops associated with frictional melting

reservoir turbidity current modeling with a two dimensional layer averaged model abstracta two dimensional layer averaged model is developed and verified to simulate turbidity current characteristics and its sluicing in reservoirs the governing equations consist of mass and momentum conservation laws for the turbidity current mixture equations for the sediment transport and bed dynamics and auxiliary relations for the interactions among clear water turbidity current and bed a finite volume unstructured polygonal mesh method is adopted so that reservoirs with complex terrains may be simulated special algorithms are developed to capture the turbidity current front movement through a clear water bed and to simulate turbidity current sluicing through reservoir outlets the developed model has been tested and verified with both conservative and nonconservative turbidity currents ranging from simple to complex reservoir terrains case studies presented include a lock exchange turbidity current with large eddy simulation and direct numerical simulation results a laboratory test of

three dimensional modeling of negatively buoyant flow in diverging channels diverging channels also known as diffusers represent common natural and industrial outlets to lakes reservoirs and rivers if the outflow in a diffuser has a larger density than the ambient water the inflow may plunge and form a density underflow in this paper a three dimensional numerical study was conducted to gain insight into the mechanism of negatively buoyant flows in diffusers with a sloping bottom of particular interest is the formation of separated flows such as wall jet and free jet flows various cases of plunging and the associated density current in a diffuser with different divergence angles and inflow densimetric froude numbers are considered the model successfully simulates the formation of attached flow wall jets and free jets in a negatively buoyant environment the onset evolution and stabilization of a stall and the subsequent development of a wall jet in a negatively buoyant flow are investigated in detail computed results also show favorable agreement with some published experimental data on density current generated by the plunging of cold water in ambient warm water in a diverging channel

whole process modeling of reservoir turbidity currents by a double layer averaged model turbidity current is formed as subaerial open channel sediment laden flow plunges into a reservoir the whole process of reservoir turbidity current i e formation propagation and recession is generally controlled by the water and sediment inputs from upstream and also the reservoir operation scheme specifying the downstream boundary condition enhanced understanding of reservoir turbidity current is critical to effective sediment management in alluvial rivers however until now there has been a lack of physically based and practically feasible models for resolving the whole process of reservoir turbidity current this is because the computing cost of three dimensional modeling is excessively high also single layer averaged models cannot resolve the formation process characterized by the transition from open channel sediment laden flow to subaqueous turbidity current or the upper clear water flow as dictated by the operation scheme of the reservoir which has significant impacts on turbidity current here a new two dimensional double layer averaged model is proposed to facilitate for the first time whole process modeling of reservoir turbidity current the two hyperbolic systems of the governing equations for the two layers are solved separately and synchronously the model is well balanced because the interlayer interactions are negligible compared with inertia and gravitation featuring a reasonable balance between the flux gradients and the bed or interface slope source terms and thus applicable to irregular topographies the model is benchmarked against a spectrum of experimental cases including turbidity currents attributable to lock exchange and sustained inflow it is revealed that an appropriate clear water outflow is favorable for turbidity current propagation and conducive to improving sediment flushing efficiency this is significant for optimizing reservoir operation schemes as applied to turbidity current in the xiaolangdi reservoir in the yellow river china the model successfully resolves the whole process from formation to recession the present work facilitates a viable and promising framework for whole process modeling of turbidity currents in support of reservoir sediment management c 2014 american society of civil engineers

numerical simulations of large scale cataclysmic floodwater a simple depth averaged model and an illustrative application a simple numerical simulation code is developed to quantitatively discuss the behaviors of past cataclysmic floods whose rigorous hydraulic descriptions would be too complex to be supported by typically available field data the code aims to keep the basic equations simple and the required computational costs low which allows greater exploration of parameter space examination of both the qualitative meaning of turbulent equations and the relative importance of terms in the shallow water equation have resulted in the adoption of the depth averaged diffusion wave approximation in two dimensions as well as manning s empirical equation for simplification on the other hand topography is included as a boundary condition since topography plays an important role in selecting flood routes the model provides important advantages over theoretical analyses or one dimensional simulations including 1 the reproduction of complicated water flow paths such as bifurcations and reconvergences 2 the reconstruction of hydrological relationships among the water paths and 3 the direct comparison among the calculated extent of the flood inundation including floodwater depths and geological and geomorphological observations preliminary reconstructions of the missoula floods demonstrate the advantages of this new approach the method of coupling field based flood information with two dimensional analysis of an entire flow path provides a basis for estimating the peak discharges and flow durations of cataclysmic megafloods on earth with direct bearing on the understanding of regional paleohydrological histories of mars

the influence of flow inertia buoyancy wind and flow unsteadiness on mixing at the asymmetrical confluence of two large rivers summary the rates and patterns of mixing of two large rivers with large density differences at a strongly asymmetrical confluence in northern spain are analyzed we assess the factors controlling the site where the denser river plunges and the mixing rates between the rivers in particular we focus on the interaction between inertial and buoyancy forces the effect of wind forcing and the unsteady nature of the hydraulic forcing the steady state location of the plunge line is shown to be controlled by an inertia buoyancy balance which accounts for the relative magnitude of the buoyancy forcing associated with density differences between the confluent rivers and the magnitudes of both the main stream and the side flow tributary inertia the plunge line moves to upstream locations as the inertia of the tributary increases for low tributary inertia and or the density contrast between the rivers increases this has important consequences for river mixing since mixing rates increase as the plunging occurs at the confluence the high mixing rates in this case occur as a result of a large mixing interface surface area and high diffusivities as the plunging area moves upstream or downstream of the confluence vertical diffusivities or the area of contact available for mixing decrease and constrain mixing rates wind forcing depending on its velocity and direction affects mixing rates through 1 altering the buoyancy inertia equilibrium and so changing the location of the plunge line 2 altering the pattern of secondary circulation within the confluence and or 3 increasing shear at the confluence flow unsteadiness can lead to changes in the location of the plunge line through time and thus can strongly modify mixing rates at the confluence the downstream movement of the plunge line is advection dominated while its upstream movement seems to respond to a baroclinic response of the confluence

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

contemporaneous plutonism and strike slip faulting a case study from the tonale fault zone north of the adamello pluton italian alps 1 a field microstructural and geochronological study of contemporaneous plutonism and strike slip faulting along the eastern tonale fault zone provides new insights into the interrelationships between magmatic emplacement contact metamorphism and shearing and it places new time constraints for the periadriatic fault system although pluton emplacement and shearing were not caused by each other they mutually interacted during contact metamorphism the character of the composite tonale fault zone varies considerably with its proximity to the northern margin of the adamello pluton from a paired greenschist facies mylonite belt northern mylonite zone and cataclastic fault zone in the west to a fault zone consisting of northern mylonite zone cataclastic fault zone and a second mylonite belt southern mylonite zone formed by contemporaneous shearing and contact metamorphism in the east ongoing strike slip motion led to telescoping and advective cooling of the deforming contact aureole new u pb zircon ages for the northernmost adamello intrusions the avio at 34 6 1 0 ma and the presanella at 32 0 2 3 ma date the onset of contact metamorphism rb sr and k ar cooling ages and new zircon fission track ages provide evidence that postintrusive cooling to below 300 c was achieved rapidly i e approximately 30 myr ago being consistent with a shallow crustal emplacement at ambient temperatures of approximately 250 c cataclastic dextral strike slip faulting continued until about 20 ma when the tonale fault zone became offset by a number of minor sinistral shears and by the giudicarie fault hence dextral strike slip motion along the periadriatic fault system east of the bergell pluton lasted from approximately 35 20 myr ago

morphology and evolution of the ejecta of hale crater in argyre basin mars results from high resolution mapping we use various data sets including images from the high resolution imaging science experiment camera hirise to examine the ejecta of the generally fresh looking hale crater that occurs in the rugged mountain terrain of nereidum montes in the northern rim materials of the argyre impact structure on mars our investigation reveals that the distal parts of the hale crater ejecta and other basin deposits behave like viscous flows which we attribute to the secondary flow of ejecta mixed with water ice rich basin materials consistent with water enrichment of the basin materials our mapping further reveals occasionally deformed surfaces including highly conspicuous features such as mounds and fractured plateaus that we interpret to be a result of periglacial modification subsequent including possibly present day to the transient localized melting and fluvial erosion caused by hale impact generated heating in particular our morphometric analysis of a well defined valley system west of hale crater suggests that it may have been formed through hydrologic glacial activity prior to the hale impact with additional modification resulting from the impact and subsequent geologic and hydrologic phenomena including glacial and periglacial activity

a perturbation solution for bingham plastic mudflows an analytical solution is proposed for laminar mudflows and debris flows that can be modeled by a bingham plastic law two dimensional unsteady nonuniform bingham flows released from a point source or a source of finite size dam break problem or mudslide problem on a steep slope are considered the method of matched asymptotic expansions was implemented to get a first order solution for the dam break problem the proposed model is found to be valid when the shock wave has advanced three reservoir lengths downstream also it is found that the bingham flow only propagates a finite distance downstream with the shock depth asymptotically approaching the yield depth and the shock velocity asymptotically falling to zero the hydrograph produced by a bingham flow is seen to have a slower and lower flood peak and a longer and higher flow tail than that produced by newtonian flow having the same dynamic viscosity comparison of the model predictions with laboratory observations shows reasonable agreement

brittle ductile brittle deformation during cooling of tonalite adamello southern italian alps abstract late to post magmatic deformation in slightly diachronous contiguous intrusions of the north western adamello batholith southern alps italy is recorded as from oldest to youngest i joints ii solid state ductile shear zones iii faults associated with epidote k feldspar veins and iv zeolite veins and faults structures ii to iv are localized on the pervasive precursory network of joints i which developed during the earliest stages of pluton cooling high temperature 500 c ductile overprinting of joints produced lineations defined by aligned biotite and hornblende on the joint surfaces and highly localized mylonites the main phase of faulting producing cataclasites and pseudotachylytes occurred at 250 c and was associated with extensive fluid infiltration cataclasites and pseudotachylytes are clustered along different e w striking dextral strike slip fault zones correlated with the activity of the tonale fault a major tectonic structure that bounds the adamello batholith to the north ductile deformation and cataclastic veining episodes occurred at p 0 25 0 3 gpa during rapid cooling of the batholith to the ambient temperatures 250 c that preceded the exhumation of the batholith timing of the sequence of deformation can be constrained by 39 ar 40 ar ages of 30 ma on pseudotachylytes and various existing mineral ages in the whole composite adamello batholith multiple magma pulses were intruded over the time span 42 30 ma and each intrusive body shows the same ductile to brittle structural sequence localized on the early joint sets this deformation sequence of the adamello might be typical of intrusions undergoing cooling at depths close to the brittle ductile transition

mesoscale linear streaks on mars environments of dust entrainment abstract variable surface albedo features on mars are likely caused by the entrainment and deposition of dust by the wind most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface some of the largest variable features here termed mesoscale linear streaks are up to 400 km in length and repeatedly occur in one of the smoothest regions of mars amazonis planitia their orientations and apparent season of variability as observed by viking and mars orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms they provide an example of the ability of large scale winds without significant local enhancement to initiate dust motion on mars the sizes and spacing of the linear streaks may be controlled by boundary layer rolls the repetitive formation of these streaks over a span of more than 11 mars years gives one measure of the stability of mars eolian processes

hirise observations of slope streaks on mars 1 images from the high resolution imaging science experiment have revealed new details on the morphologic and topographic characteristics of slope streaks on mars over 1500 hirise images were analyzed with 78 unique image sites having slope streaks images with low sun illumination reveal that dark slope streaks have topographic relief where streaked surfaces are lower than their surroundings slope streaks often initiate below localized features such as rock outcrops individual boulders and impact craters they are also abundant in great numbers within the blast zones of small young impact craters 10 50 m in diameter these observations suggest that slope streaks can be triggered by localized disturbances such as rockfalls and impact blasts seismic activity from external e g impacts or internal forces could also trigger slope streaks the topographic relief and triggering mechanisms of slope streaks seem to best fit models that involve dry dust avalanches martian slope streaks and meters thick avalanche scars are part of a continuum of active mass wasting features at meter to sub meter scales

three decades of slope streak activity on mars slope streaks are surficial mass movements that are abundant in the dust covered regions of mars targeting of slope streaks seen in viking images with the mars orbiter camera provides observations of slope streak dust activity over two to three decades in all study areas new and persisting dark slope streaks are observed slope streaks disappeared in one area with persisting streaks nearby new slope streaks are found to be systematically darker than persisting streaks which indicates gradual fading far more slope streaks formed at the study sites than have faded from visibility the rate of formation at the study sites was 0 03 new slope streaks per existing streak per mars year bright slope streaks do not presently form in sudden events as dark slope streaks do instead bright streaks might form from old dark slope streaks perhaps transitioning through a partially faded stage

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

geologic settings of martian gullies implications for their origins 1 martian gullies are found on steep slopes of all origins on all sorts of terrains of all ages scattered across nearly all of mars gullies are observed on all manner of substrates layered massive shattered rubble with or without nearby mantling deposits gullies are most common in the southern midlatitudes but also occur in the northern hemisphere in near polar terrain on equatorial volcanoes and on northern plains most gullies in the southern hemisphere are on south facing slopes but they occur on slopes of all orientations gullies are among the youngest features on mars but locally are overlain by eolian deposits and cut by faults old or eroded gullies are rare and those found have been partially stripped from slopes leaving no rock debris behind most gully deposits contain no detectable rocks these data are inconsistent with published hypotheses of gully formation including seeps and breakouts of water or brine hydrothermal activity cryovolcanism and breakouts from liquid carbon dioxide the data are consistent with gullies being dry flows of eolian material dust and silt comparable to climax snow avalanches on earth eolian sedimentation should be correlated little with underlying geology cause of slope age of terrain type of terrain or the nature of the rocks eolian sedimentation should be correlated with wind deceleration which will cause suspended sediment to drop and areas with common gullies are those with strong wind deceleration predicted by global circulation model in such areas sediment will be deposited preferentially in the lee of obstacles for the gully rich areas of the southern midlatitudes winds blow from the nnw so that sediment is deposited on sse facing slopes i e poleward these predictions are in accord with observations

geomorphological evidence for a dry dust avalanche origin of slope streaks on mars mars has several different types of slope feature that resemble aqueous flows however the current cold dry conditions are inimical to liquid water resulting in uncertainty about its role in modern surface processes dark slope streaks were among the first distinctive young slope features to be identified on mars and the first with activity seen in orbital images they form markings on steep slopes that can persist for decades and the role of water in their formation remains a matter of debate here i analyse the geomorphic features of new slope streaks using high resolution orbital images comparison of images before and after streak formation reveal how this process affects the surface and provides information about the cause these observations demonstrate that slope streaks erode and deposit material in some instances they also reveal that streaks can jump slopes and may be erosive very near their termini these observations support a formation model where dark slope streaks form as ground hugging low density avalanches of dry surface dust such streaks need not be treated as special regions for planetary protection patterns of erosion and deposition by some slope streaks on mars are consistent with a dry dust avalanche origin according to an analysis of orbital images before and after new streaks formed

origin of hydrous fluids at seismogenic depth constraints from natural and experimental fault rocks abstract fluids control the mechanical behavior of fault zones during the seismic cycle we used geochemical mineralogical microstructural hydrogen isotope compositions and fourier transform infrared ftir investigations to characterize the origin of hydrous fluids involved in ductile and brittle shear zones at the bottom of the seismogenic crust natural samples were collected from exhumed mylonitic shear zones and cataclasite pseudotachylyte bearing faults in the northern adamello italian southern alps which were active at 9 11 km depth pseudotachylytes solidified coseismic friction induced melts testify to ancient seismogenic behavior of the faults natural pseudotachylytes were compared with artificial pseudotachylytes produced in high velocity friction experiments simulating seismic slip mylonites have mineralogical elemental and hydrogen isotope compositions 80 d 78 similar to the host tonalite 77 d 73 within the analytical error of 5 cataclasites have instead mineralogical chlorite epidote k feldspar no biotite major and trace elements enrichment in k2o ba rb depletion in cao na2o sio2 and hydrogen isotope 69 d 60 compositions suggesting interactions with a crustal metamorphic fluid pseudotachylytes are composed of high temperature minerals plagioclase biotite dmisteinbergite cordierite and scapolite and have elemental compositions resulting from mixing of tonalite and cataclasite pseudotachylytes have complex microstructures including i microlitic domains with well crystallized micrometric biotite which have hydrogen isotope composition 81 d 59 similar to cataclasites and tonalite and ii cryptocrystalline domains with poorly crystallized biotite which have very high water content release water upon heating at t 50 c and have low d value 93 the hydrogen isotope composition of bulk samples is dominated by the composition of cryptocrystalline domains 103 d 88 where most of the water is hosted their hydrogen isotope composition is compatible with adsorption of present day rainfall water d 95 artificial pseudotachylytes have the same hydrogen isotope compositions of the starting tonalite 76 d 74 or cataclasite 68 d 62 with a slight decrease of the d values in some samples 85 d 81 the first ingression of a crustal metamorphic fluid occurred in cataclastic faults natural pseudotachylytes when not contaminated by present day rainfall water have a hydrogen isotope composition similar to tonalite and cataclasite as reproduced in dry high velocity friction experiments the fluids dissolved in coseismic melts are most likely derived from the breakdown of hydrous minerals of cataclasite and tonalite undergone melting and we could not identify the infiltration of an external fluid during earthquakes

dynamics of unusual debris flows on martian sand dunes 1 gullies that dissect sand dunes in russell impact crater often display debris flow like deposits in their distal reaches the possible range of both the rheological properties and the flow rates are estimated using a numerical simulation code of a bingham plastic flow to help explain the formation of these features our simulated results are best explained by a rapid debris flow for example a debris flow with the viscosity of 102 pa s and the yield strength of 102 pa can form the observed deposits with a flow rate of 0 5 m3 s sustained over several minutes and total discharged water volume on the order of hundreds of cubic meters which may be produced by melting a surface layer of interstitial ice within the dune deposits to several centimeters depth

meter scale slopes of candidate mer landing sites from point photoclinometry photoclinometry was used to analyze the small scale roughness of areas within the proposed mars science laboratory msl landing ellipses the landing ellipses presented in this study are those in eberswalde crater gale crater and holden crater the mawrth vallis site could not be measured due to its albedo variations we were able to constrain surface slopes on length scales comparable to the hirise image resolution 0 25 meters pixel the msl mission has various engineering constraints that each candidate landing ellipse must satisfy these constraints indicate that the statistical value of the slopes at one two and five meter baselines are an important criterion we used our technique to estimate surface slopes across large swaths of each image and built up slope statistics for the images in each landing ellipse we are confident that all three final msl landing site ellipses that could be measured in this study are within the small scale roughness constraints our results have provided input into the landing hazard assessment process

debris flows over sand dunes on mars evidence for liquid water 1 this study focuses on the formation and physical properties of the gullies observed over large martian dunes especially those of the russell crater 54 s 347 w geomorphic features like sinuosities and connections of the channels show that gullies over dunes involve flows with a significant proportion of liquid the occurrence of levees implies that these flows are debris flows with a yield strength characteristics of bingham plastic materials we apply terrestrial methods to estimate viscosity and velocity of these flows from levee size and sinuosities we obtain average velocities in the range of 1 to 7 m s 1 and apparent viscosities of 2 8 to 46 000 pa s with an average at 740 pa s compared with the 0 001 pa s of pure water these viscosities and velocities are in the range of terrestrial debris flows with a proportion of 10 to 40 of h2o these properties are typical of water holding debris flows but not of pure water surface runoff or co2 driven flows the debris flows over dunes are oriented on south facing slopes like other recent gullies meltwater from ground ice formed during a recent period of high obliquity is the more likely explanation for the formation of such flows over dunes

dilatancy induced fluid pressure drop during dynamic rupture direct experimental evidence and consequences for earthquake dynamics abstract fluid pressure and flow in the crust are key parameters controlling earthquake physics since earthquake slip is linked to spatio temporal localisation of deformation it is expected that the local fluid pressure around the fault plane could potentially impact the dynamic strength of the slipping fault zone coseismic fluid pressure drops have been inferred from field studies notably in gold deposits which are thought to be formed by this process but reliable quantitative predictions are still lacking here experimental results are presented where local on and off fault fluid pressure variations were measured in situ during dynamic rock fracture and frictional slip under upper crustal stress conditions during the main rupture the on fault fluid pressure dropped rapidly to zero indicating partial vaporisation and or degassing further deformation produced stick slip events systematically associated with near instantaneous drops in fluid pressure providing direct experimental support of the concept of seismic suction pump in situ fluid volume and wave speed measurements together with microstructural investigations show that dilatancy is the process driving fluid pressure drops during rupture and slip extrapolation of the laboratory results indicate that dilatancy induced fluid pressure drops might be a widespread phenomenon in the crust counteracting thermal pressurisation as a weakening mechanisms in freshly fractured rock

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

effect of water and rock composition on re strengthening of cohesive faults during the deceleration phase of seismic slip pulses abstract the elastic strain energy release rate and seismic waves emitted during earthquakes are controlled by the on fault temporal evolution of the shear stress during rupture propagation high velocity friction experiments highlighted that shear stress on the fault surface evolves rapidly during seismic slip pulses this temporal evolution of shear stress is controlled by both fault weakening at seismic slip initiation and re strengthening rate towards the end of slip while numerous studies focused on fault weakening less attention was given to co seismic re strengthening processes here we performed 53 friction experiments normal stress 30 mpa slip rate 6 5 m s 1 imposing constant slip acceleration and deceleration 7 8 m s 2 on cohesive carrara marble 99 calcite and micro gabbro silicate built rock under dry vacuum and water pressurized conditions microstructural observations showed that micro gabbro accommodated seismic slip by bulk melting of the sliding surfaces whereas carrara marble by coupled decarbonation and grain size dependent crystal plastic processes under room humidity conditions and low imposed power density i e product of normal stress per slip rate re strengthening rate during the deceleration stage was up to 17 times faster in marble than in micrograbbro in the latter the re strengthening rate increased slightly with the power density the presence of water enhanced further this trend on the contrary in marbles the re strengthening rate decreased drastically with power density and in the presence of water our experimental observations highlighted the first order importance of the mineralogy and rheology of the slip zone materials and to a second order of the presence of water in controlling co seismic re strengthening of faults during seismic slip deceleration

regional dust deposits on mars physical properties age and history major dust storms on mars play an important role in the deposition and removal of fine dust material thermal radar and visual remote sensing observations provide important constraints on the martian regolith which have been used to determine the location and physical properties of regional dust deposits these deposits are located in three northern equatorial regions tharsis 20 s to 50 n 60 to 190 w arabia 5 s to 30 n 300 to 360 w and elysium 10 to 30 n 210 to 225 w they are covered by fine 2 40 m bright albedo 0 27 particles with fewer exposed rocks and coarse deposits than found elsewhere dust is currently deposited uniformly throughout the equatorial region at a rate of 40 m global storm over geologic time the rate of accumulation may vary from 0 to 250 m yr due to changes in atmospheric conditions produced by orbital variations dust deposited during global storms is subsequently removed only from dark regions resulting in a net accumulation in the low inertia bright regions the thickness of these current dust deposits is 0 1 2 m the thermal inertia places a lower limit of 0 1 m on the thickness of these deposits while the sparse but ubiquitous presence of exposed rocks and the degree of visible mantling indicate that the thickness is less than 5 m dual polarization radar observations of a very rough texture in tharsis are consistent with this model with a 2 m thick dust layer burying most of the surface rocks but permitting radar sampling of the rough subsurface based on their thickness and rate of accumulation the age of these deposits is 105 106 years suggesting a cyclic process of deposition and removal one possible cause may be cyclic variations in the magnitude and location of maximum wind velocities related to variations in mars orbit at present perihelion and maximum wind velocities occur in the south whereas regional dust deposits occur in the north suggesting net transport from south to north orbital parameters oscillate with periods ranging from 5 104 to 106 years the agreement between these periods and the dust deposit age suggests a possible link at different stages in orbit evolution maximum wind velocities will occur in the north with subsequent erosion and redistribution of the accumulated fines based on this model much of the uppermost martian surface is very young and is being continually reworked

mixing and circulation at the confluence of two rivers entering a meandering reservoir 1 a field data set collected under different conditions is analyzed to characterize the spatial arrangement of two large inflows ebro and segre with distinct physical chemical characteristics as they join at the upstream end of ribarroja reservoir in northern spain given the short average residence time of water in the reservoir the spatial arrangement of the rivers at their confluence and their mixing rates are likely the drivers of the stratification patterns observed near the dam in winter inflows have similar densities 0 o 10 5 and their spatial distribution is largely determined by inertial forces and in particular by the discharge ratio downstream of the confluence both rivers flow side by side and largely unmixed over long distances in summer with 0 of o 10 3 the flow fields at the confluence are largely controlled by buoyancy forces atmospheric forcing during strong wind events and centrifugal forces caused by the meandering shape of the reservoir induce significant tilting of the isotherms leading to localized high mixing rates mixing in general though is weak at this time of the year in fall and early winter density differences are largely controlled by conductivity differences between the incoming flows the warmer ebro water with larger thermal inertia flows beneath the colder segre water the spatial arrangement of the inflows is largely controlled by the discharge ratio and mixing between sources is strong likely as a result of mixed water being denser than either of the incoming flows

coseismic damage and softening of fault rocks at seismogenic depths abstract elastic stiffness a critical property for stress orientation propagation of earthquake ruptures and associated seismic waves and the capability of crustal rocks to store strain energy is expected to be highly variable throughout the seismic cycle due to complex sequences of damage and healing post seismic healing and exhumation related alteration render it impossible to assess how well rock stiffness as measured in the laboratory on samples collected from fault zones represents in situ coseismic rock stiffness at seismogenic depths here we estimate the in situ coseismic stiffness of fault rocks from the pseudotachylyte bearing gole larghe fault zone italian southern alps using aspect ratio measurements of pseudotachylyte injection veins and numerical simulations aspect ratios of injection veins cutting across tonalite and cataclasite exhibit a maximum vein aperture positively correlating with vein length to model vein opening fault and injection veins are assumed to be filled with pressurized melt consistent with recent results from studies of melt lubrication we assume that the magnitude of the melt pressure is in equilibrium with the fault normal stress and the fault vein approximately maintains constant thickness during slip the numerical simulations of injection vein opening due to pressurized frictional melt indicate that the average in situ coseismic stiffness of the wall rocks is 5 50 times smaller than the stiffness obtained from laboratory measurements on the same rocks in their present day state the disagreement between laboratory measurements and simulations brings into question the appropriateness of using laboratory derived values for rock stiffness to model coseismic processes at depth

thermal pressurization and slip weakening distance of a fault an example of the hanaore fault southwest japan a controversy over the last decade is the large difference in the slip weakening distance d c between laboratory measured and seismically estimated values our numerical analyses of the thermal pressurization process based on measured transport properties of the hanaore fault zone in japan reveal that the process is effective for this fault and that d c becomes of the order of several decimeters to about 1 m when the width of the deformation zone is less than 10 20 mm this d c value is of exactly the same order as that determined seismically so thermal pressurization can be a mechanism for solving the d c paradox the thermal pressurization process effectively reduces the heat production rate and the temperature rise expected for this fault zone is at most about 600 c which is not high enough a temperature to melt rocks

discovery of a widespread low latitude diurnal co2 frost cycle on mars while the detection of co2 ice has only been reported outside the martian polar regions at very high elevation i e elysium olympus mons and the tharsis montes nighttime surface observations by the mars climate sounder on board the mars reconnaissance orbiter document the widespread occurrence of atmospherically corrected ground temperatures consistent with the presence of extensive carbon dioxide frost deposits in the dusty low thermal inertia units at middle low latitudes thermal infrared emissivities interpreted in conjunction with mass balance modeling suggest micrometer size co2 ice crystals forming optically thin layers never exceeding a few hundreds of microns in thickness i e 10 2 kg m 2 locally which is insufficient to generate a measurable diurnal pressure cycle 0 1 of the martian atmosphere atmospheric temperatures at middle low latitudes are not consistent with precipitation of co2 ice suggesting that condensation occurs on the surface the recurring growth and sublimation of co2 ice on martian dusty terrains may be an important process preventing soil induration and promoting dynamic phenomena soil avalanching and fluidization and regolith gardening maintaining a reservoir of micrometer size dust particles that are mobile and available for lifting the discovery of this diurnal co2 cycle represents an important step forward in our understanding of the way the martian atmosphere interacts with the surface

fast slip with inhibited temperature rise due to mineral dehydration evidence from experiments on gypsum anomalously low heat flow around active faults has been a recurrent subject of debate over past decades we present a series of high velocity friction experiments on gypsum rock cylinders showing that the temperature of the simulated fault plane is efficiently buffered due to large scale endothermic dehydration reaction the tests were performed at 1 mpa normal stress and a velocity of 1 3 m s 1 while measuring the temperature close to the sliding surface and the relative humidity around the sample the temperature close to the sliding surface is remarkably stable at 100 c during the dehydration reaction of gypsum microstructural and x ray diffraction investigations show that dehydration occurs at the very beginning of the test and progresses into the bulk as slip increases in the hottest parts of the sample anhydrite crystal growth is observed the half thickness of the dehydrated layer ranges from 160 m at 2 m slip to 5 mm at 68 m slip thermodynamic estimates of the energy needed for the dehydration to occur yield values ranging from 10 to 50 of the total mechanical work input the temperature plateau is thus well explained by the energy sink due to the dehydration reaction and the phase change from liquid water into steam we suggest that similar endothermic reactions can efficiently buffer the temperature of fault zones during an earthquake this is a way to explain the low heat flow around active faults and the apparent scarcity of frictional melts in nature

aureole deposits of the martian volcano olympus mons the aureole of grooved terrain that surrounds the large shield volcano olympus mons consists of several overlapping roughly circular sheets each 0 5 to 1 5 km thick the surfaces of these materials bear abundant curvilinear ridges and troughs 10 to 100 km long and 1 to 5 km wide which form anastomosing patterns that vary in length and width over the aureole the aureole is asymmetric to olympus mons extending almost 1000 km northwest from the center of the volcano but only 600 km southeast the lobate form of the deposits the pressure ridges on their surfaces and the deflection of aureole material around barriers indicate that the deposits were emplaced as viscous flows high resolution viking orbiter pictures show the aureole material to be unstratified and it is inferred to contain randomly distributed large dark blocks whose weathering products form dark streaks in the talus on the flanks of ridges a pyroclastic origin is proposed for the aureole the following sequence is suggested at least six great pyroclastic eruptions occurred prior to the construction olympus mons they formed very fluid ash flows that became viscous during late stages of emplacement and pressure ridges formed on the surfaces of the deposits before they finally came to rest the oldest and most extensive aureole deposit finely grooved terrain was considerably modified by erosion prior to being partly covered by later eruptions a positive gravity anomaly over the olympus mons area may define the site of a near surface magma chamber that was the source of the pyroclastic eruptions

the role of the wind transported dust in slope streaks activity evidence from the hrsc data abstract slope streaks are gravity driven albedo features observed on martian slopes since the viking missions the debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting a systematic mapping of slope streaks from the high resolution stereo camera is presented in this paper two regions known for their slope streaks activity have been studied the first one is located close to cerberus lava flow and the second one is inside the olympus mons aureole the statistics of slope streaks shapes measured from orthorectified images confirm previous results from mars orbiter camera surveys preferential orientations of slope streaks are reported slope streaks occur preferentially on west facing slopes at latitudes lower than 30 n for olympus and on south west facing slopes for cerberus wind directions derived from a general circulation model during the dusty season correlate with these orientations furthermore west facing slopes at olympus have a thicker dust cover these observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow the paucity of slope streaks at high latitudes and their preferential orientation on south facing slopes have been presented as an evidence for a potential role of h 2 o phase transition in triggering or flow the potential role of h 2 o cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations the role of h 2 o might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes 30 n 33 n and on all slopes further north

a bingham plastic model for a muddy seabed under long waves the dynamics of cohesive mud under wave action is important to the geological processes along some coastlines because of the complex rheological properties there have been vastly different models for predicting the effect of mud on wave attenuation this paper focuses on a non newtonian behavior of highly concentrated mud whereby shearing strain occurs only if the shear stress exceeds a certain threshold called the yield stress the wave induced motion in a thin mud layer beneath a clear water layer is studied there are circumstances in which the yield stress is dominant and acts like a coulomb friction mud motion can change from continuous to intermittent as the wave attenuates the effects of the non newtonian behavior on wave damping are compared to other more common causes of dissipation

onset of underflow in slightly diverging channels experiments are conducted in a horizontal laboratory channel with slightly diverging walls to simulate buoyancy driven plunging flow a temperature difference between inflow and downstream ambient provides the density differential that initiates the underflow temperature profiles and flow visualization are used to determine flow conditions in the plunge region channel divergence angles half angles from 1 15 are investigated volumetric flow rates in the sinking flow increase from 0 45 during the plunging process maximum entrainment rates are nearly linearly related to divergence angle depths of the underflow downstream from the plunge line are from 0 65 0 9 times the depth at the plunge line densimetric froude numbers from 0 56 0 89 occur at the plunge line depending on the channel divergence angle and the discharge densimetric froude number a flow analysis that explains and supports the experimental data is presented channel expansion affects the plunging process significantly particularly e

flow paths and spatial heterogeneity of stream inflows in a small multibasin lake we describe the flow paths of negatively buoyant river inflows in a small lake with multiple basins separated by sills toolik lake alaska using field data and three dimensional simulations comparisons of field observations analytical computations and simulations show that in small basins in which the timescale for filling f is less than the timescale of an event 0 overflow is the dominant mechanism of interbasin exchange exchange is mediated by internal wave displacements if upwelling reaches the height of the sills zs this criterion is met if the lake number the inverse of which is proportional to the degree of metalimnetic tilting is less than zi zi zs where zi is the vertical displacement of the intrusion entrainment followed by horizontal dispersion is the dominant mechanism of interbasin transport and can account for 65 of the exchange between large subbasins entrainment is enhanced when submerged sills force river water to flow close to the surface layer depths of intrusions depend upon discharge they occurred in the lower metalimnion for the coldest events analyzed but were near the top of the metalimnion during low discharge events such as during brief cold fronts persistence of intrusions depends upon the time interval between cold fronts they ranged from a few days to three weeks timescales of horizontal mixing vary with meteorological forcing they ranged from on the order of 1 d for wind events with speeds of up to 6 8 m s 1 to on the order of 10 d for light winds

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

note on the analysis of plunging of density flows this note is devoted to the correction of an error in a calculation contained in a classical published paper on the plunging of river flows as they enter lakes or reservoirs the correction of the error provides a felicitous result according to which not only the ratio of underflow thickness just after plunging to depth just before plunging but also the densimetric froude numbers both just before and just after plunging are all specified as a function of a single parameter this single parameter characterizes the tendency of plunging to entrain ambient water into the density underflow

numerical simulations of flood basalt lava flows roles of parameters on lava flow morphologies using a three dimensional numerical simulation model of lava flow we studied the effects of parameters on the morphologies of simple flood basalt lava flows the model can provide a more realistic description of morphologies of lava flows than two dimensional models because it can evaluate the complex relationship between erupted volume and length of lava by considering lateral spreading of flows moreover our model can calculate lava morphologies on a very moderate slope or even on a flat plane without mesh direction dependency it can simulate not only small scale flows on individual volcanoes but also large scale 100 km flows without numerical instability although the length of a lava flow is controlled by many parameters including rheological properties and eruption rate the length is not a simple function of these parameters we confirm that small changes in parameters such as slope angle and viscosity can affect the length of the flow increasing the eruption rate up to 107 m3 s makes basaltic lava flows longer however at eruption rates higher than 107 m3 s on 0 3 slopes flow length does not increase beyond that of the 107 m3 s eruption rate due to volume conservation of erupted lava thus eruption conditions cannot be estimated from the length of a lava flow alone therefore the estimated eruption rate obtained by previous two dimensional models which essentially estimate eruption rate from the length of the flow will not always reveal useful values on the other hand the width of a simple lava flow is a good measure of its eruption rate because the width is mainly controlled by the eruption rate and yield strength a simple lava whose width is greater than 100 km was almost certainly emplaced at eruption rates higher than 107 m3 s if the yield strength of the flow is in a basaltic range

pathways of river water to the surface layers of stratified reservoirs this study uses tracer experiments to characterize the fate of a cold plunging river into a mediterranean reservoir under different stratification conditions three tracer experiments in lake beznar spain demonstrate that a significant fraction of the inflow may be quickly entrained into the surface mixed layer sml rather than flowing to lower depths we observe that a fraction and possibly all of river inflow entrains into the sml when the density current forms intrusions at the top of the metalimnetic layer intrusions near the base of the sml form due to lighter interfacial fluid at the top of the density current with intermediate properties between river reservior water when there is sufficient dilution of the cold inflow and abrupt density changes at the base of the sml consequently a layer of fluid splits from the denser part of the current and intrudes just below the sml while any remaining fluid flows to lower depths we parameterize this splitting behavior in terms of the transition richardson number ri12 2 1 0 1 where 0 1 and 2 are densities of the inflow the sml and the metalimnetic layer underneath respectively and is the total dilution through the plunge zone and subsequent entrainment splitting occurs when ri12 1 consistent with previous laboratory experiments we use this theory to predict the seasonal fate of river water during the stratification of lake beznar and identify the conditions that favor the formation of intrusions near the base of the sml

earthquake slip weakening and asperities explained by thermal pressurization for the earth s crust to release accumulated stress in the form of an earthquake a fault must weaken and give way otherwise the movement would quickly grind to a halt due to the surrounding pressure this weakening is not really understood laboratory experiments simply don t match seismologists estimates of the distance a fault must slip before it becomes very weak a new study concludes that the missing ingredient is water geological studies and measurements show the slip zones to be narrow impermeable structures water already in the fault zone can quickly become pressurized by frictional heating as the rocks start to move catalysing large earthquakes from minor movements an earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion1 2 this slip weakening occurs over a critical distance dc understanding the controls on dc in nature is severely limited however because the physical mechanism of weakening is unconstrained conventional friction experiments typically conducted at slow slip rates and small displacements have obtained dc values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes3 4 5 6 here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the median tectonic line fault zone japan we show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid7 8 9 10 is the slip weakening mechanism our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity

recognition classification and mechanical description of debris flows abstract various types of flow or mass movement involving water and sediments occur on steep slopes in mountainous areas among them debris flows are peculiar events during which a large volume of a highly concentrated viscous water debris mixture flows through a stream channel throughout the world these phenomena cause considerable damage but remain poorly understood although a basic knowledge is already available concerning their recognition and propagation firstly a synthesis of the useful practical criteria of recognition is proposed debris flows must be seen as intermediate phenomena between hyperconcentrated flows intense bed load transport and landslides separated from them by sharp transitions of some characteristics celerity deposit nature and flow type two parameters solid fraction and material type thought to be appropriate for a sound and practical classification are brought out and the corresponding complete classification of flow and mass movements in mountain areas is presented two extreme debris flow types are thus distinguished muddy debris flows and granular debris flows a critical review of recent advances in debris flow dynamic is then proposed it is pointed out that adequate work must be carried out in the field of non newtonian fluid mechanics in particular one fundamental rheological property of debris flow materials is the yield stress which explains thick deposits on steep slopes and can be inferred from field measurements furthermore it can be used to estimate viscous dissipation within the bulk during flow relevant models predicting muddy debris flow dynamics are already available whereas further progress is needed concerning granular flows

coupling an underflow model to a three dimensional hydrodynamic model a separate underflow model is coupled to the three dimensional 3d estuary and lake computer model the underflow equations are solved on a two dimensional 2d grid underlying the 3d model grid the underflow model entrains ambient water whose properties are given by the fluid properties of the bottom boundary cells in the 3d model this new approach allows improved representation of underflow effects in z coordinate models by reducing numerical convective entrainment an idealized case is used to illustrate the benefits of the underflow model comparisons of model results and field data for a saline underflow event in lake ogawara and a cold water underflow in lake kinneret demonstrate improved model capability in representing underflow events that are thin compared to the vertical grid scale

liquid co2 breakout and the formation of recent small gullies on mars we show that the action of a co2 suspended flow could have produced the recent small gullies on mars and hence that liquid water is not required the model involves the build up of a liquid co2 aquifer behind and below a dry ice barrier dam cap rock in the pore spaces a few meters into the rock from the cliff face and on order of a hundred meters below the top of the cliff brink surface seasonal or obliquity cycle seasonal heating causes pinching out of the dry ice barrier and rapid release of the liquid co2 erosion of the gullies occurs as the rapid vaporization of the liquid co2 with entrainment of rock and clathrate hydrate ice produces a density flow analogous to a terrestrial nue ardente

slope streaks on mars correlations with surface properties and the potential role of water the mars orbiter camera on board the mars global surveyor spacecraft has returned images of numerous dark streaks that are the result of down slope mass movement occurring under present day martian climatic conditions we systematically analyze over 23 000 high resolution images and demonstrate that slope streaks form exclusively in regions of low thermal inertia confirming earlier results steep slopes and remarkably only where peak temperatures exceed 275 k the northernmost streaks which form in the coldest environment form preferentially on warmer south facing slopes repeat images of sites with slope streaks show changes only if the time interval between the two images includes the warm season surprisingly in light of the theoretically short residence time of h 2o close to the surface the data support the possibility that small amounts of water are transiently present in low latitude near surface regions of mars and undergo phase transitions at times of high insolation triggering the observed mass movements

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

stability and localization of rapid shear in fluid saturated fault gouge 1 linearized stability analysis field observations of major earthquake fault zones show that shear deformation is often confined to principal slipping zones that may be of order 1 100 m wide located within a broader gouge layer of order 10 100 mm wide this paper examines the possibility that the extreme strain localization observed may be due to the coupling of shear heating thermal pressurization and diffusion in the absence of a stabilizing mechanism shear deformation in a continuum analysis will collapse to an infinitesimally thin zone two possible stabilizing mechanisms studied in this paper are rate strengthening friction and dilatancy for rate strengthening friction alone a linear stability analysis shows that uniform shear of a gouge layer is unstable for perturbations exceeding a critical wavelength using this critical wavelength we predict a width for the localized zone as a function of the gouge properties taking representative parameters for fault gouge at typical centroidal depths of crustal seismogenic zones we predict localized zones of order 5 40 m wide roughly consistent with field and experimental observations for dilatancy alone linearized strain rate perturbations with a sufficiently large wavelength will undergo transient exponential growth before decaying back to uniform shear the total perturbation strain accumulated during this transient strain rate localization is shown to be largely controlled by a single dimensionless parameter e which is a measure of the dilatancy of the gouge material due to an increase in strain rate

dynamic weakening and amorphization in serpentinite during laboratory earthquakes the mechanical properties of serpentinites are key factors in our understanding of the dynamics of earthquake ruptures in subduction zones especially intermediate depth earthquakes here we performed shear rupture experiments on natural antigorite serpentinite which showed that friction reaches near zero values during spontaneous dynamic rupture propagation rapid coseismic slip 1 m s although it occurs over short distances 1 mm induces significant overheating of microscale asperities along the sliding surface sufficient to produce surface amorphization and likely some melting antigorite dehydration occurs in the fault walls which leaves a partially amorphized material the water generated potentially contributes to the production of a low viscosity pressurized melt explaining the near zero dynamic friction levels observed in some events the rapid and dramatic dynamic weakening in serpentinite might be a key process facilitating the propagation of earthquakes at intermediate depths in subduction zones

numerical model of turbidity currents with a deforming bottom boundary a numerical model of turbidity currents with a deforming bottom boundary has been developed the model predicts the vertical structure of the flow velocity and concentration as well as change in the bed level due to erosion and deposition of suspended sediment the reynolds averaged navier stokes equations for dilute suspension have been solved using a finite volume method the bottom boundary and the grid system are allowed to adjust in response to sediment deposition and entrainment during the computation the model has been applied to simulate the evolution of a conservative saline density current and turbidity currents along an 11 6 m long flume that includes a slope followed by a horizontal bed the model successfully simulates the evolution of the currents model results have been compared with the experimental data good similarity profiles of velocity and excess density or suspended sediment concen tration are obtained at both the upstream supercritical and the downstream subcritical flow regions a turbulent schmidt number larger than one has been found to be appropriate for providing a good match with the experimental data changes in bed level predicted by the model have also been found to be in agreement with the experiment data

shallow viscoplastic flow on an inclined plane evolving viscoplastic flows upon slopes are an important idealization of many flows in a variety of geophysical situations where yield stress is thought to play a role for such models asymptotic expansions suitable for slowly moving shallow fluid layers lubrication theory reduce the governing equations to a simpler problem in terms of the fluid thickness we consider the version of the theory for fluids described by the herschel bulkley constitutive law and provide a variety of solutions to the reduced equation both numerical and analytical for extruded inclined domes we derive the characteristic temporal behaviour of measures of the dome s dimensions

topographic measurements of slope streaks on mars abstract slope streaks are enigmatic actively forming albedo features occurring on slopes in high albedo low thermal inertia dust rich equatorial regions on mars they are a specifically martian phenomenon with no direct analogs on the earth their morphology suggests that the streaks are initiated at their upslope tips and propagate down to their termini however the physical mechanism of their formation is uncertain we performed a large series of measurements of slopes associated with slope streaks using stereo pairs of high resolution orbital images obtained by hirise camera and generated several digital elevation models for selected streaks we found that 1 slopes at the upslope streak tips range widely however there is a strong indication that streaks can be initiated only on slopes steeper than 20 2 slopes of the streak termini show an even wider range with some streaks terminating at slopes as steep as their tips while others propagate all the way down to horizontal surfaces 3 the streaks can propagate stably for long many hundreds of meters distances and can turn following the topographic gradient on 10 15 slopes 4 no uphill propagation of streaks is detected over baselines of tens of meters 5 the slope streaks often propagate over 1 2 m high obstacles and can climb 1 2 m uphill over short meters distances we used these findings to assess the viability of two classes of hypotheses about slope streak formation mechanisms proposed earlier 1 dry some kind of run away avalanche like dry granular flow and 2 wet some kind of run away propagation of a front of percolating brines in the shallow subsurface no specific observation unambiguously proves or rejects either of the two mechanisms several of our findings are readily explained by the dry mechanism and cannot be easily explained with any kind of wet mechanism while other findings are closely consistent with the wet mechanism and are difficult to reconcile with the dry mechanism this situation might be explained by equifinality meaning that the streaks despite their similarity are formed by different physical processes alternatively some modifications to either the dry or wet mechanisms may be able to provide a coherent explanation it is also possible that new ideas are needed to understand the processes involved

geological and hydrological histories of the argyre province mars the geologic history of the multi ringed argyre impact basin and surroundings has been reconstructed on the basis of geologic mapping and relative age dating of rock materials and structures the impact formed a primary basin rim materials and a complex basement structural fabric including faults and valleys that are radial and concentric about the primary basin as well as structurally controlled local basins since its formation the basin has been a regional catchment for volatiles and sedimentary materials as well as a dominant influence on the flow of surface ice debris flows and groundwater through and over its basement structures the basin is interpreted to have been occupied by lakes including a possible mediterranean sized sea that formed in the aftermath of the argyre impact event the hypothesized lakes froze and diminished through time though liquid water may have remained beneath the ice cover and sedimentation may have continued for some time at its deepest the main argyre lake may have taken more than a hundred thousand years to freeze to the bottom even absent any heat source besides the sun but with impact induced hydrothermal heat geothermal heat flow due to long lived radioactivities in early martian history and concentration of solutes in sub ice brine liquid water may have persisted beneath thick ice for many millions of years existence of an ice covered sea perhaps was long enough for life to originate and evolve with gradually colder and more hypersaline conditions the argyre rock materials diverse in origin and emplacement mechanisms have been modified by impact magmatic eolian fluvial lacustrine glacial periglacial alluvial colluvial and tectonic processes post impact adjustment of part of the impact generated basement structural fabric such as concentric faults is apparent distinct basin stratigraphic units are interpreted to be linked to large scale geologic activity far from the basin including growth of the tharsis magmatic tectonic complex and the growth into southern middle latitudes of south polar ice sheets along with the migration of surface and sub surface volatiles towards the central part of the primary basin the substantial difference in elevation with respect to the surrounding highlands and tharsis and the thaumasia highlands result in the trapping of atmospheric volatiles within the basin in the form of fog and regional or local precipitation even today in addition the impact event caused long term millions of years hydrothermal activity as well as deep seated basement structures that have tapped the internal heat of mars as conduits for far greater time possibly even today this possibility is raised by the observation of putative open system pingos and nearby gullies that occur in linear depressions with accompanying systems of faults and fractures long term water and heat energy enrichment complemented by the interaction of the nutrient enriched primordial crustal and mantle materials favorable to life excavated to the surface and near surface environs through the argyre impact event has not only resulted in distinct geomorphology but also makes the argyre basin a potential site of exceptional astrobiological significance

numerical investigation of plunging density current when a buoyant inflow of higher density enters a reservoir it sinks below the ambient water and forms an underflow downstream of the plunge point the flow becomes progressively diluted due to the fluid entrainment the entrainment rate is strongly dependent on the richardson number and reaches a constant value well downstream of the plunge point this study is concerned with the analysis of the plunging phenomenon and the determination of the entrainment a k e model including buoyancy effects both in a sloping and a diverging channel is used to reproduce the main flow characteristics a relation between the depth at the plunge point in a channel of constant width and in a diverging channel is established and theoretical results for the calculation of the dense layer thickness are provided the latter indicates that the spreading rate of the dense layer in a diverging channel is a function of both the entrainment rate and the channel width the predictions of the plunge line location are in agreemen

mechanical amorphization flash heating and frictional melting dramatic changes to fault surfaces during the first millisecond of earthquake slip the evolution of fault strength and behavior during the initial stages of slip plays an important role in driving the onset of instability and fault weakening using small displacement triaxial experiments on quartz sandstone this study highlights the rapid onset of microstructural change on fault interfaces and identifies new evidence for an evolution in physical processes with increasing slip and velocity pre ground fault surfaces have been slipped over a range of velocities 0 36 m s 1 to 18 cm s 1 and at normal stresses comparable to upper to mid crustal conditions 92 287 mpa microstructural analysis of the fault interfaces reveals the formation of amorphous material at displacements 170 m and slip durations 1 ms mechanical and microstructural observations have been combined with numerical modeling to present the first documented examples of a transition from mechanical amorphization to flash heating then frictional melting with changes in slip conditions the sequence of processes activated during the initial stages of fault movement may provide new insights into factors that influence the onset of slip in the seismogenic crust

rheology and topography control the path of a lava flow insight from numerical simulations over a preexisting topography 1 determination of flow path is strongly controlled by both the preexisting topography and rheology of the lava flow using the okmok 1997 eruption as an example lava flow we perform numerical simulations of bingham fluids flowing over preexisting topography and find that flow rheology determines whether or not new lobe formation or bifurcation occurs from the main flow at a topographic divide or remains confined by local topography therefore lobe or branch length may increase for higher viscosity flows when considering the effect of topographic control also even one order of magnitude difference in the rheological properties allows lava flows to move in completely different paths which may suggest that flow bifurcation due to topographic control provides insight to the local rheological properties of a lava flow the effect reported here should be taken into account in risk assessments of future volcanic hazards

recent debris flows on mars seasonal observations of the russell crater dune field 1 debris flows occur on slopes in the russell crater dune field the morphology of the erosion features resembles terrestrial viscous slurry flows mudflows and suggests that a flow of fine grained material mixed with liquid water might have been responsible for their formation seasonal mgs tes and moc imagery based observations of the dune field show 1 an annual frosting and defrosting cycle and 2 that liquid h2o could be stable within a limited time period in the summer of the southern hemisphere these observations lead to the conclusion that debris flows in the russell crater dune field may form under current climatic conditions by episodic or seasonal melting of small amounts of autumn winter condensed water ice

two different supply styles of crater outflow materials on venus inferred from numerical simulations over dems abstract the three dimensional numerical simulation code for nonisothermal bingham fluid was applied to four typical crater outflows on venus to estimate emplacement styles of outflow materials we have succeeded in reproducing emplacement features qualitatively over digital elevation models dems obtained by the magellan spacecraft and we have shown that outflow materials can be formed by melts of basaltic crust therefore the presence of crater outflows may not be evidence of the presence of previously suggested fluid materials such as komatiite or carbonatite although we failed to model the very low viscosity flow numerically estimated supply rates of flow materials are categorized into two types a catastrophic style and a gentle style markham and isabella crater outflows are examples of catastrophic styles and the flow materials required to form them were probably supplied at higher rates than 1010 m3 s and the durations of material supply were less than 100 s this very high supply rate is difficult to attribute to any volcanic process because typical eruption rates of terrestrial volcanic flows are less than 8 or 9 orders of magnitude lower than that such a style of emplacement is more plausibly considered as a result of the impact itself for example a catastrophic debris flow or a vapor cloud triggered by the impact on the other hand supply rates of willard and xantippe outflows which are considered gentle style flows were estimated to be about 104 m3 s and the durations were more than 105 s such a gentle style of outflow emplacement is probably not a direct result of the impact but is rather due to a secondary process possibly segregation and drainage of impact melt materials from within previously emplaced ejecta materials or post impact volcanism

negatively buoyant flow in diverging channel iii onset of underflow if they are negatively buoyant denser than ambient water inflows to lakes and reservoirs sink plunge below the water surface after entering the location of the plunge line or maximum penetration into the lake or reservoir is related to the ratio of inertial to buoyant forces and lake or reservoir geometry experiments have been conducted in diverging horizontal laboratory channels and the plunging phenomenon has been reproduced for flows separating from the channel wall the relationship xp b0 0 52f04 has been found to describe the maximum horizontal penetration xp the basic form and exponent of this relation was developed from jet flow theory and the coefficient was experimentally determined f0 is the inflow densimetric froude number and b0 is the inflow channel width experimental data for xp b0 are also reported for attached flows in this case the distance to plunging can be expressed as xp b0 0 74f0 0 5 tan 1

modeling a plunging underflow a coupled three dimensional hydrodynamics and two dimensional underflow model is adapted to provide simulation of plunging inflows in reservoirs the new approach accounts for the effect of the barotropic term prior to the plunge point of the inflow simulations of plunging flows in constant width and constant slope channels are conducted and the resulting plunge depths are in agreement with prior empirical models simulation of a previously measured underflow in wellington reservoir australia demonstrates the model application to a plunging inflow in a natural water body and good agreement between field and model results

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

energy dissipative plunging flows the analysis of plunging flows using energy dissipation hypothesis is presented in this paper the classic two control volume theory has recently been found questionable and needs to be corrected in this study we avoid the questionable part of that framework and use a single control volume for the analysis of plunging flows furthermore we hypothesize that the increase in kinetic energy in the underflow and entrained flow should be no greater than the loss in potential energy as the inflow plunges in the current framework the entrained flow rate does not exceed approximately 40 of the total inflow rate the densimetric froude number at the plunge point fdp q g hp3 where q inflow rate per unit width g reduced gravity of inflow and hp flow depth at the plunge point is typically in the range of 0 3 fdp 0 6 for plunging flows in a constant width channel

mass movement within a slope streak on mars 1 slope streaks on mars represent a currently active geological process various theories for slope streak formation have suggested that slope streaks form by disturbing only a thin surface veneer or by staining of the surface preserving pre existing topography within the streak theories also vary as to whether the formation mechanism requires the presence of water or another liquid we present observations of a slope streak that reveal topographic mounds within the streak these mounds do not continue outside the streak and we suggest that they formed with or immediately after the slope streak we use estimates of the total volume of mounds in this particular streak compared with the estimated excavation volume to extrapolate to a global sediment transport rate from slope streak formation if this slope streak is typical then this calculated rate is greater than estimates of the total volume of material transported by dust storms each year

thermochemical pressurization of faults during coseismic slip 1 during earthquakes frictional heating on the fault plane induces a temperature rise and thus a pore pressure rise which is known as thermal pressurization tp coseismic mineral dehydrations may occur because of this temperature increase and are included within the tp framework dehydrations are modeled as a source term for pore pressure because of the total volume change and as a sink term for temperature because they are endothermic the reaction occurs within the slipping zone when a threshold temperature ts is reached dehydration reaction kinetic is modeled using a first order reaction rate using energy and fluid mass conservation we derive analytically the equations of evolution of pore pressure temperature and reaction extent in the undrained adiabatic case using a constant reaction rate we investigate the values of the kinetic rate constant required to produce a significant effect which are much higher than laboratory data reported in the literature on clay serpentine and phyllosilicate dehydration we show however that such high values can be reached if the temperature dependency of the rate constant is taken into account next we include fluid and heat transport and use an arrhenius law to calculate the rate constant as a function of temperature the subsequent set of differential equations is then solved numerically the main effect of dehydration reactions is an increase of pore pressure and a stabilization of the temperature during slip we explore a wide range of parameters in order to determine in which cases dehydration can be considered as a nonnegligible process for high permeability rocks 10 18 m2 and when the amount of water that can be released is of the order of 10 dehydration is an important mechanism as it delays the onset of melting which would normally occur even within the tp framework if the onset temperature is low compared to the initial temperature t0 ts t0 150 c overpressure can occur if the reactions are highly endothermic and if their kinetic is fast enough frictional melting would not occur unless the dehydration reactions are completed within the slipping zone

metastability of liquid water on mars abstract a simple model of local heat transport on mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal incidence insolation an experiment has been performed to confirm the model of evaporation rate at low pressure reduction of radiative cooling due to gully geometry is shown to be important since appropriate meteorological topographic and optical conditions may occur on slopes nearly anywhere on the planet hydrological features such as gullies would likely form only where such ice might accumulate notably in sheltered locations at high latitudes it is suggested that cold trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies

putative ice flows on europa geometric patterns and relation to topography collectively constrain material properties and effusion rates europa s surface exhibits numerous small dome like and lobate features some of which have been attributed to fluid emplacement of ice or slush on the surface we perform numerical simulations of non newtonian flows to assess the physical conditions required for these features to result from viscous flows our simulations indicate that the morphology of an ice flow on europa will be at least partially influenced by pre existing topography unless the thickness of the flow exceeds that of the underlying topography by at least an order of magnitude three classes of features can be identified on europa first some possibly most putative flow like features exhibit no influence from the pre existing topography such as ridges although their thicknesses are generally on the same order as those of ridges therefore flow processes probably cannot explain the formation of these features second some observed features show modest influence from the underlying topography these might be explained by ice flows with wide ranges of parameters ice temperatures 230 k effusion rates 10 7 m 3 year 1 and a wide range of grain sizes although surface uplift e g by diapirism and in situ disaggregation provide an equally compelling explanation third several observed features are completely confined by pre existing topographic structures on at least one side these are the best known candidates for flow features on europa if these features resulted from solid ice flows then temperatures 260 k and grain sizes 2 m are required such small grain sizes seem unlikely low viscosity flows such as ice slurries or brines provide a better explanation for these features our results provide theoretical support for the view that many of europa s lobate features have not resulted from solid ice flows

slope streak formation and dust deposition rates on mars 1 the mars orbiter camera moc has imaged sometimes repeatedly mass movements known as slope streaks which are abundant in the dust covered regions on mars they are among the few known examples of contemporary surface changes a survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of 7 per existing streak per martian year either there is a complete turnover within a few decades or the streak population is currently increasing rapidly large spatial as well as possible temporal variations in the formation rate are obtained from these data streaks do not appear to fade over time periods comparable to their inverse formation rate of 28 years as seen by analysis of viking orbiter images containing streaks that are still visible in moc images gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate and its current imbalance with the fading rate

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh